Abstract:
A transceiver module comprised of a multiplexing/demultiplexing optical subassembly is provided. The optical subassembly includes either a transmitter module or a receiver module or both. The transmitter module has laser diodes emitting optical signals, which are reflected by reflectors, and coupled together by thin film filter. The receiver module includes thin film filters that decouple a received optical signal into constituent components. These components are reflected by reflectors to photo detectors by which the optical signals are converted into electrical signals. The reflector are capable of dual axis adjustment for adjustment of inclination thereof to effect active alignment. Further, the transmitter module and the receiver module define positioning recesses to position the laser diodes and photo detectors. The recesses are sized in accordance with the wavelengths associated with the laser diodes and photo detectors to effect passive alignment.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to an optical transceiver module, and in particular to an optical subassembly of the optical transceiver module, featuring small size, high precision alignment, and excellent coupling efficiency.  
         [0003]     2. The Prior Arts  
         [0004]     Optical fiber transmission is instrumental in the development of many advanced applications for telecommunications and data communications. This high bandwidth transmission needs local fiber access to provide two-way communications to the home through an optical transceiver, which is composed of a driver circuit, an electrical subassembly (ESA), and an optical subassembly (OSA). Operation frequency plays a critical role in determining the transmission speed. Conventionally, high speed transmissions up to 10 Gb/sec, 40 Gb/sec, or even higher, is realized by increasing the operation frequency of the transmitter driver circuit, which inevitably leads to a significant increase of manufacturing costs.  
         [0005]     Wavelength Division Multiplexing (WDM) was developed to enhance the transmission speed of optical fiber system without undesirably increasing the operation frequency and thus effectively limiting the increase of manufacturing costs. The WDM solution allows an optical transceiver to multiplex a plurality of optical signals of different wavelengths onto a “mixed” signal that can travel along a single optical fiber. Such a “mixed” signal, once reaching a destination receiver, is demultiplexed and separated with the constituent component of the desired wavelength retrieved. In other words, the WDM technology optimizes the utilization of transmission bandwidth by permitting simultaneous transmission of optical signals of different wavelengths over a single optical fiber. Two types of WDM are known, namely Dense Wavelength-Division Multiplexing (DWDM) and Coarse Wavelength-Division Multiplexing (CWDM), based on the minimum size of the spacing between wavelengths of the optical signals that can be composed into the single “mixed” signal.  
         [0006]     For DWDM, the normal spacing between two bands of different wavelengths is in the range of 0.8-1.6 nm, so that unitary bandwidth can support extremely high optical signal density. C-band that operates in a bandwidth of 1525-1565 nm is most commonly used for long haul, MAN and LAN signal transmission. Due to the dense arrangement of optical signals in a single band, optical splitters and photo coupler modules that are employed for DWDM must be upgraded. In addition, a thermo-electric cooler (TEC) that is expensive is needed to control the operation temperature of a laser diode that emits the desired optical signals whereby micro-drifting of the wavelength of the optical signals can be eliminated to ensure transmission quality. All these add to the manufacturing costs, as well as power consumption.  
         [0007]     On the other hand, Coarse Wavelength-Division Multiplexing (CWDM) arranges less optical signals in a single optical fiber, which allows for a large spacing (20 nm) between wavelengths of the optical signals. This wavelength spacing is much larger than that of the DWDM. Thus, CWDM does not require the expensive thermoelectric cooler (TEC) to reduce the operation temperature of the laser diode nor to prevent the drifting of the bandwidth.  
         [0008]     Although CWDM has a transmission capacity lower than DWDM, such a drawback can be easily overcome by using a number of laser diodes of lower transmission speeds employing CWDM to simultaneously transmit optical signals, and a high-speed transmission device compared with DWDM can be realized. For example, to meet a transmission requirement of 10 Gb/sec, CWDM only needs several laser diodes with lower transmission speed, for example laser diodes of 3.125 Gb/sec or 2.5 Gb/sec, which by the nature thereof are more stable in signal transmission, to produce the equivalent performance as a laser diode of 10 Gb/sec. As another example, to reach up to 40 GB/sec transmission, four laser diodes of 10 Gb/sec or slightly higher baud rates together can meet the required specifications. This method can be expanded for even higher transmission bandwidths.  
         [0009]     The use of laser diodes of the transmitter optical subassembly (TOSA) with lower transmission speeds allows the sensing area of the corresponding photo diodes on the receiver optical subassembly (ROSA) to be increased. Therefore, the alignment tolerance is less critical and the coupling efficiency between optical signals and optical fiber can be improved.  
         [0010]     Also, using laser diodes with lower transmission speeds makes the design for the electrical subassembly (ESA) and driver circuit less critical, but the more challenging part is the design of the optical subassembly (OSA), which is to combine optical signals of different wavelengths and couple them onto a single optical fiber (the part of TOSA), or to separate multiplexed optical signals on the receiver end of the optical fiber into optical wavelength signals to respective photo detectors (the part of ROSA), and at the same time the design spec has to meet the Multi Source Agreement (MSA) and the module miniaturization.  
         [0011]     Coupling efficiency for a number of optical signals of different wavelengths is of vital importance in reducing signal loss in optical transmission and in reducing the misalignment among each component. Passive alignment is commonly employed to simplify the manufacturing process. The passive alignment is done by forming a mating portion on the body of an optical subassembly. The mating portion is machined with high precision. An optical device with a counterpart mating portion, which is also precisely machined, is inter-engaging with the mating portion of the body. Since both mating portions are of high machining precision, the coupling efficiency is enhanced. However, since machining precision is subject to limitation, the improvement of coupling efficiency is also subject to limitation. Thus, for precise alignment, the mating means must be of extremely high manufacturing precision and this inevitably complicates the manufacturing process and increases the manufacturing costs.  
         [0012]     On the other hand, an active alignment technique allows for adjustment of the position of an optical device with respect to an optical transmitter or receiver in order to obtain an optimum coupling therebetween after the optical device is mounted to the transmitter or receiver. An example of active alignment is illustrated in U.S. patent application Ser. No. 10/971,462 and its Taiwanese counterpart, Taiwan Patent Application No. 93118803. The coupling efficiency can be optimized by means of the after-mounting adjustment and flexibility can be provided for manufacturing/assembling of the optical transmitter and receiver.  
         [0013]     For an optical transmitter or receiver that transmits or receives a number of optical signals of different wavelengths, a number of laser diodes or photo detectors. Each laser diode or photo detector must have an individual base for independent adjustment, which leads to a bulky size of the optical transmitter or receiver.  
         [0014]     Thus, the present invention is aimed to provide an optical subassembly that overcomes the above-discussed drawbacks of the conventional optical subassemblies.  
       SUMMARY OF THE INVENTION  
       [0015]     Thus, an objective of the present invention is to provide an optical transceiver module featuring both passive alignment and active alignment so that poor alignment precision of laser diodes and photo detectors in the conventional optical subassembly can be eliminated and effectively enhancing coupling efficiency of the optical subassembly.  
         [0016]     Another objective of the present invention is to provide an optical transceiver module having a simple and compact structure for miniaturization of the optical transceiver module.  
         [0017]     In accordance with the present invention, to realize the above objectives, an optical transceiver module comprised of a multiplexing and demultiplexing optical subassembly is provided. The optical subassembly comprises either a transmitter module or a receiver module or both. The transmitter module comprises four laser sources, respectively giving off optical signals of different wavelengths, which after collimated, are reflected by respective reflectors to the same plane on which the optical signals are coupled together by means of thin film filters, which coupled signal is then transmitted through an optical fiber. The receiver module comprises thin film filters that decouple a received optical signal into constituent components. These components are reflected by respective reflectors to photo detectors by which the optical signals are converted into corresponding electrical signals. The reflectors are capable of dual axis adjustment for adjustment of inclination thereof to effect active alignment. Further, the transmitter module and the receiver module comprise a body in which positioning recesses of predetermined dimension are formed to receive and position the laser diodes and photo detectors. The dimensions of the recesses are determined in accordance with the wavelengths associated with the laser diodes or photo detectors thereby effecting passive alignment. Thus, both passive alignment and active alignment can be done for the optical module of the present invention to optimize the coupling efficiency.  
         [0018]     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, preferred embodiments in accordance with the present invention. In the drawings: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is an exploded view of an optical subassembly constructed in accordance with the present invention, which is embodied as an optical transmitter module;  
         [0020]      FIG. 2  is a perspective view of a body of the optical transmitter module of the present invention;  
         [0021]      FIG. 3  is another perspective view of the body of the optical transmitter module taken from a bottom side of the body;  
         [0022]      FIG. 4  is a perspective view of an adjustor of the optical subassembly in accordance with the present invention;  
         [0023]      FIG. 5  is an exploded view of the adjustor of the present invention;  
         [0024]      FIG. 6  is a cross-sectional view of the optical transmitter module of  FIG. 1 , showing spatial relationship between a light source generation device and the body of the optical transmitter module; and  
         [0025]      FIG. 7  is an exploded view of an optical subassembly constructed in accordance with the present invention, which is embodied as an optical receiver module;  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]     A preferred embodiment of the present invention will be described with reference to the attached drawings for explanation of the structure and function of an optical subassembly constructed in accordance with the present invention. It is, however, noted that the optical subassembly of the present invention can be embodied in both an optical transmitter module and an optical receiver module and an optical module that simultaneously comprises an optical transmitter module and an optical receiver module, such as an optical transceiver module. In the following, a description with respect to an optical receiver module will be given first.  
         [0027]     With reference to the drawings and in particular to  FIG. 1 , which shows an exploded view of an optical subassembly constructed in accordance with the present invention embodied in an optical transmitter module, which is broadly designated with reference numeral  100 , the optical transmitter module  100  comprises a body  102  having top and bottom surfaces  104 ,  106 . A light source generation device  300  is mounted to the bottom surface  106  of the body  102 .  
         [0028]     Also referring to  FIGS. 2 and 3 , which show perspective views of he body  102  from top and bottom sides, respectively, in the embodiment illustrated, the body  102  comprises a flat body of which the top and bottom surfaces  104 ,  106  are opposite to and substantially parallel to each other with bores  108  extending through the flat body and running between the top and bottom surfaces  104 ,  106 . The number of the bores  108  is four in the embodiment illustrated, but it can be other numbers such as eight. Each bore  108  is substantially normal to the top and bottom surfaces  104 ,  106  and extending from the top surface  104  to the bottom surface  106 . The bores  108  serve as passageways for light beams, which will be further described.  
         [0029]     The bottom surface  106  has a periphery along which a circumferential flange  110  is formed. The flange  110  and the bottom surface  106  together form a space for receiving the light source generation device  300 . Inboard the area surrounded by the circumferential flange  110 , the bottom surface  106  defines a positioning recess  112  corresponding to each bore  108 . The positioning recesses  112  are defined in the bottom surface  106  but not extending to the top surface  104 , while the bores  108  extend completely through the body  102  from the bottom surface  106  to the top surface  104 . As mentioned above, four bores  108  are defined in the body  102  and thus, four positioning recesses  112  are defined in the bottom surface  106 .  
         [0030]     The light source generation device  300  comprises a base  302 , which is comprised of a circuit board on which a control circuit is formed. The base  302  is shaped and sized in correspondence with to the receiving space defined by the circumferential flange  110  of the bottom surface  106  of the body  102  and is thus snugly received in the receiving space. The base  302  is secured in the receiving space with suitable means, such as a notch  114  defined in an inside surface of the circumferential flange  110  and a projection  304  formed along an edge of the base  302  and press-fit or force-fit into the notch  114  to secure the base  302  to the bottom surface  106  of the body  102 . Other means, such as adhesives that fix the base  302  inside the circumferential flange  110 , may also be employed. Since this is generally known to those having ordinary skills, no further detail is needed herein.  
         [0031]     The light source generation device  300  comprises a light generator  306  corresponding in position to each positioning recess  112 . The light generator  306  has a shape and size receivable in the corresponding positioning recess  112 . Each light generator  306  comprises a light source  308 , such as a laser diode, which emits a laser beam. The laser diodes  308  are positioned to align with the bores  108  respectively whereby the laser beams emitted from the laser diodes  308  are allowed to travel through the bore  108  and reaching the top surface  106  of the body  102 .  
         [0032]     In the embodiment illustrated, a collimating device  116  is arranged at a suitable location inside or above each bore  108 . The collimating device  116  collimates the laser beam emitted from the laser diode  308  and thus is generally spaced from the laser diode  308  at a suitable distance for collimating and thus forming parallel beam of the laser beam from the laser diode  308 . The collimating device  116  may be comprised of a single lens, such as a ball lens or an aspheric lens, or a combination of a number of lenses. To simplify the description hereafter, the collimating device  116  may be interchangeably replaced the term “lens”. The lens or lenses of the collimating device  116  may be coated with a wavelength-selecting anti-reflection optical film to reduce reflection loss. This is also familiar to those having ordinary skills in the art of optics and thus no further detail is needed herein.  
         [0033]     The lens or lenses that constitute the collimating device  116  can be fixed inside or above the bore  108  of the body  102  by light-curable adhesives, such as ultra-violent curable adhesives, heat-curable adhesives, or other adhesives. Alternatively, glass-to-metal sealing technique can be employed to fix the collimating device  116  to the body  102 . Another alternative is the molded the lens or lenses of the collimating device  116  with the body  102  if the body  102  is made of plastic injection molding.  
         [0034]     Also referring to  FIGS. 4 and 5 , a reflector  118  corresponding in position to the bore  108  and aligning with each collimating device  116  is mounted to the top surface  104  of the body  102 . The reflector  118  comprises a reflection surface that is inclined at an inclination angle with respect to a central axis of the corresponding bore  108  to reflect the light beam traveling through the bore  108  to a desired direction, which will be further described hereinafter. In accordance with the present invention, each reflector  118  is mounted to the top surface  104  of the body  102  in an adjustable manner by an adjustor  120 , which features active alignment. In the embodiment illustrated, the adjustor  120  comprises a first adjusting member  122 , serving as a vertical adjusting element, and a second adjusting member  124 , serving as a horizontal adjusting element. The reflector  118  is mounted to the second adjusting member  124 . The reflector  118  can be integrally formed with the second adjusting member  124  or the reflector  118  is a separate part externally attached to the second adjusting member  124 . The first and second adjusting members  122 ,  124  are rotatable about respectively rotation axes  126 ,  128 , as indicated by arrows A, B of  FIG. 4 , for adjustment of the orientation of the reflector  118  and thereby changing the direction along which the laser beam is reflected by the reflector  118  for realizing active alignment.  
         [0035]     In the embodiment illustrated, the first adjusting member  122  comprises a first cylinder  130 , having a central axis coincident with the rotation axis  126  of the first adjusting member  122  to serve as a pivot for the first adjusting member  122 . The first pivot  130  is rotatably fit into a circular hole  132  that is defined in the top surface  104  of the body  102  at a location adjacent the bore  108  whereby the adjustor  120  is mounted on the top surface  104  in such a manner that the adjustor  120  is rotatable about the rotation axis  126 . In the embodiment illustrated, the rotation axis  126  is substantially normal to the top surface  104  and thus the first adjusting member  122 , which features adjustment of the adjustor  120  about a vertical axis, is rotatable about an axis that is perpendicular to the top surface  104 . However, it is apparent that the rotation axis  126  is not necessarily perpendicular to the top surface  104 , and can be inclined with respect to the vertical direction at any desired angle. The adjustor  120  comprises a second pivot  134  coincident with the rotation axis  128  about which the second adjusting member  124  is rotatable. In this respect, the second adjusting member  124  forms a bore  136  into which the second pivot  134  rotatably fits. Thus, the second adjusting member  124  is rotatable about the rotation axis  128  with respect to the first adjusting member  122 . Alternatively, a bore can be defined in the first adjusting member with a central axis of the bore perpendicular to the rotation axis of the first adjusting member and the second adjusting member  124  comprises a pivot extending therefrom and fit into the bore, which realizes relative rotation of the second adjusting member  124  with respect to the first adjusting member  122 .  
         [0036]     In the embodiment illustrated, the second pivot  134  is substantially parallel to the top surface  104  of the body  102  and thus the second adjusting member  124 , which features adjustment of the reflector  118  about a horizontal axis, is rotatable about a rotation axis parallel to the top surface  104 . It is apparent that the second rotation axis  128  is not necessarily parallel to the top surface  104  and can be inclined with respect to the top surface  104  at any desired angle. However, it is noted that the second pivot  134  is better not parallel to the first pivot  130  in order ensure rotation adjustment of the reflector  118  about two non-parallel axes. In the embodiment illustrated, the rotation axis  126  of the first pivot  130  is substantially normal to the rotation axis  128  of the second pivot  134 .  
         [0037]     The rotatability of the first and second adjusting members  122 ,  124  about respective rotation axes  126 ,  128  with respect to the body  102  allows for the adjustment of the position and orientation of the reflector  118  with respect to the top surface  104  of the body  102 , thereby realizing active alignment of the reflector  118 . This will be further described.  
         [0038]     Although in the embodiment illustrated, the position and the orientation of the reflector  120  are adjustable by the rotation about the first and second pivots  130 ,  134 , it is also possible to carry out adjustment of the reflector  118  by means of rotation about a single pivot.  
         [0039]     In practice, friction of predetermined magnitude is present between the first pivot  130  and the hole  132  of the body  102 , and also present between the second pivot  134  and the bore  136  of the second adjusting member  124 . The friction helps retaining relative positions among the first adjusting member  122 , the second adjusting member  124 , and the body  102  after the adjustment of the first and second adjusting members  122 ,  124  is done by rotating the members  122 ,  124  about the first and second pivots  130 ,  134 . If necessary, the first and second adjusting members  122 ,  124  can be further secured by means of for example adhesives applied between the first adjusting member  122  and the second adjusting member  124 , and between the body  102  and the first adjusting member  122 , or resistance welding or laser welding can be employed to permanently secure the members  122 ,  124  on the top surface  104  of the body  102 .  
         [0040]     A wall  138 , comprised of a number of sections, is formed on the top surface  104  of the body  102 , which wall delimits an internal space  140  having four inner faces each defining a through hole  142  corresponding in position to each reflector  118  whereby the laser beam reflected by the reflector  118  travels in a direction directly through the through hole  142  to enter the internal space  140 . A passage  144  is formed in the wall  138  and in communication with the internal space  140 . A receptacle or connector  146  is fixed to the body  102  in front of the passage  144  for releasable connection with an external optical fiber (not shown) through which optical signals are received by and transmitted from the optical subassembly  100  of the present invention. A passage lens  148  is mounted in the receptacle  146  to guide laser beam that is transmitted from the optical subassembly  100  into the optical fiber, or to guide the laser beam that is received by the optical subassembly  100  from the optical fiber into the internal space  140  in which further processing is performed.  
         [0041]     The receptacle  146  is fixed to the passage  144  of the body  102  by light-curable adhesive, such as ultraviolet curable adhesives, heat-curable adhesives, or other adhesives or by other known means, such as laser spot welding and resistance welding.  
         [0042]     Further, the receptacle  146  that connects the external optical fiber can be an optical connector of any type, such as LC connector, SC connector, FC connector, or other types. This is known to those having ordinary skills of the field of optical communication and thus no further detail is needed herein.  
         [0043]     A thin film filter  150  is attached to the inner faces of the wall  138  at a position opposing each through hole  142 , which serves as a reflector in the optical transmitter module. With the reflection of the thin film filters  150 , the laser beams traveling through hole  142  into the internal space  140  are reflected at least once to move in a direction through the passage  144 , transmitting through the passage lens  148  to enter the optical fiber connected to the receptacle  146 .  
         [0044]     The operation of the optical transmitter module in accordance with the present invention will be described now with reference to  FIG. 1 . The first light generator  306  on the base  302  of the light source generation device  300  generates and emits a first laser beam of first wavelength λ 1 . The first laser beam transmits through the collimating device  116  in the corresponding bore  108  of the body  102  to form a collimated parallel light beam. The collimated first laser beam is then reflected by the reflector  118  of associated adjustor  120  to run through the associated through hole  142  of the wall  138  to enter the internal space  140 . The first laser beam is then reflected by the first thin film filter  150  to couple to a second laser beam, which as a wavelength of λ 2 , generated by the second light generator  306  of the light source generation device  300 . The combined first and second laser beams is then reflected by the second thin film filter  150  to couple with a third laser beam, which as a wavelength of λ 3 , generated by the third light generator  306  of the light source generation device  300 . The combined first, second, and third laser beams is then reflected by the third thin film filter  150  to couple with a fourth laser beam, which as a wavelength of λ 4 , generated by the fourth light generator  306  of the light source generation device  300 . The first, second, third, and fourth laser beams are thus combined as a single optical signal that passes through the passage  144  and transmits through the passage lens  148  to be coupled to the optical fiber connected to the receptacle  146 . The coupling of optical signals in an optical transmitter module is known, such as that described in Taiwan Patent Application No. 93118803 of which a U.S. counterpart application bears Ser. No. 10/971,462, and thus no further detail is needed herein.  
         [0045]     Also referring to  FIG. 6 , the optimum distance between the laser diode  308  and the collimating device  116  is different for laser beams of different wavelengths. Thus, the positioning recesses  112  of the body  102  are provided with optimum depths d 1 , d 2 , d 3 , and d 4  when the body  102 , which has a unitary structure, is manufactured. The optimum distances are different for the wavelengths of the laser beams emitted from the laser diodes  308  are different and the depths are set and corrected in advance in accordance with the wavelength of the laser beam emitted from the associated laser diode  308  whereby the laser beams that transmitted through the collimating devices  116  can be collimated by the associated collimating devices  116  with the optimum collimation result, which provides parallel laser beams. This realizes passive alignment of the optical subassembly of the present invention.  
         [0046]     In addition to the passive alignment, the present invention also features active alignment, which is realized by the dual-axis rotation based adjustment of the adjustor  120  that adjusts the position and orientation of the associated reflector  118  to compensate error or tolerance of assembling optical devices or components, such as lens, thin film filter, receptacle, base of light source generation device. This ensures the optimum coupling efficiency of the optical subassembly in accordance with the present invention.  
         [0047]     With reference to  FIG. 7 , a description of an optical receiver module that embodies the present invention will be given as another embodiment of the present invention. The optical receiver module of the present invention is broadly designated with reference numeral  500 , which, similar to the optical transmitter module  100  that has just been described hereinabove, comprises a body having a construction identical to that of the optical transmitter module  100 . Thus, the body and associated or related parts and components thereof will be designated with the same reference numerals as those in the optical transmitter module  100  and related description will be omitted for simplicity. The optical receiver module  500  comprises a photo detection device, generally designated with reference numeral  700 , which takes the position of the light source generation device  300  in the above-described optical transmitter module  100 . Similarly, the photo-detection device  700  is received and fixed in a receiving space below the bottom surface  106  of the body  102  and thereby mounted to the body  102  to form the optical receiver module  500  in accordance with the present invention.  
         [0048]     The photo-detection device  700  comprises a base  702 , which is comprised of a circuit board on which a control circuit is formed. The base  702  is shaped and sized in correspondence with to the receiving space defined by the circumferential flange  110  of the bottom surface  106  of the body  102  and is thus snugly received in the receiving space. The base  702  is secured in the receiving space with suitable means, such as a notch  114  defined in an inside surface of the circumferential flange  110  and a projection  704  formed along an edge of the base  702  and press-fit or force-fit into the notch  114  to secure the base  702  to the bottom surface  106  of the body  102 . Similar to the optical transmitter module  100 , other means, such as adhesives that fix the base  702  inside the circumferential flange  110 , may also be employed to secure the photo-detection device  700  to the body  102 .  
         [0049]     The photo-detection device  700  comprises a photodetector  706  corresponding in position to each positioning recess  112  of the body  102 . The photodetector  706  has a shape and size receivable in the corresponding positioning recess  112 . Each photodetector  706  comprises an optical sensing element  708 , such as a photo diode, which detects optical signals, such as a laser beam, and generates a corresponding electrical signal. The photo diodes  708  are positioned to align with the bores  108  respectively to detect and receive optical signal applied thereto through the bores  108 .  
         [0050]     The operation of the optical receiver module in accordance with the present invention will now be described. Optical path along which optical signals or laser beams to be received by the optical receiver module  500  travel is exactly opposite to that of the optical transmitter module  100 . An optical signal comprised of a number of different wavelengths, such as first wavelength (λ 1 ), second wavelength (λ 2 ), third wavelength (λ 3 ), and fourth wavelength (λ 4 ), is transmitted into the optical receiver module  500  through an external optical fiber connected to the receptacle  146 . The multiple-wavelength optical signal is transmitted through the passage lens  148 , which converts the optical signal into parallel ray that is guided through the passage  144  into the internal space  140 . The parallel ray is incident onto a first one of the four thin film filter  150 , which separates a first light component of the optical signal that has the wavelength λ 4  from the other components of the optical signal and allows the first light component to travel toward the reflector  118  of the associated adjustor  120 . The reflector  118  re-directs the first light component toward the associated collimating device  116 , which converges the light onto the photo diode  708  of the first photodetector  706  and an electrical signal is generated by the photo diode  708  in association with the first light component.  
         [0051]     Meanwhile, the remaining components are reflected and redirected by the first one of the thin film filters  150  to the second one of the thin film filters  150 , which separate a second component of the optical signal, which has the wavelength λ 3 , from the optical signal. The second light component is redirected by the associated reflector  118  toward the associated collimating device or lens  116  and converged onto the photo diode  708  of the associated photodetector  706 . An electrical signal in association with the light component of wavelength λ 3  is generated by the photo diode  708 .  
         [0052]     The remaining components, namely wavelengths λ 2  and λ 1 , are reflected and redirected by the second one of the thin film filters  150  to the third one of the thin film filters  150 , which separates a third component of the optical signal, which has the wavelength λ 2 , from the optical signal. The third light component is redirected by the associated reflector  118  toward the associated collimating device or lens  116  and converged onto the photo diode  708  of the associated photodetector  706 . An electrical signal in association with the light component of wavelength λ 2  is generated by the photo diode  708 .  
         [0053]     The remaining component of wavelength λ 1  is reflected and redirected by the third one of the thin film filters  150  to the fourth one of the thin film filters  150 , through which the light component of wavelength λ 1  transmits and travels toward the associated reflector  118 , which redirects the light component through the associated collimating device or lens  116  and converged onto the photo diode  708  of the associated photodetector  706 . An electrical signal in association with the light component of wavelength λ 1  is generated by the photo diode  708 . Thus, all four component of the incoming optical signal are converted into associated electrical signals, which can be subsequently processed in any desired manners.  
         [0054]     Since the wavelengths of the four components are different, and since the difference among the optical paths along which the four components travel, the optimum distance between each collimating lens  116  and corresponding photodetector  706  is different from each other. Similar to the case of optical transmitter module  100  that was described above, the optical receiver module  500  can set the optimum depth d 1 , d 2 , d 3 , and d 4  of the positioning recesses  112  in advance for passive alignment. Also, the optical receiver module  500  of the present invention allows for dual-axis rotation based adjustment of the adjustor  120  that adjusts the position and orientation of the associated reflector  118  to compensate error or tolerance of assembling optical devices or components, such as lens, thin film filter, receptacle, base of light source generation device, whereby active alignment is realized. The capability of both passive and active alignments effectively compensates errors or tolerances caused in assembling process of the receiver module and ensures the optimum coupling efficiency of the optical subassembly.  
         [0055]     Embodiments associated with individual optical receiver module and optical transmitter module have been described hereinabove. It is apparent to those having ordinary skills of the art to combine these embodiments together to form an optical subassembly that features both transmission and reception of optical signals, while possessing the advantages provided by the active and passive alignments in accordance with the present invention.  
         [0056]     It is apparent that the present invention has at least the followings advantages:  
         [0057]     (1) The optical subassembly of the present invention provides a novel design of optical path, which effectively shortens the length of the optical path and thus making the subassembly compact. The novel design, together with active alignment, allows for active adjustment to enhance the coupling efficiency of the optical transceiver module.  
         [0058]     (2) The active alignment provided by the present invention effectively compensates errors of assembling and manufacturing optical parts, such as lens, thin film filter, optical fiber receptacle or connector, and bases for laser diode device and photo detector device.  
         [0059]     (3) The present invention provides optimum coupling efficiency for light sources of different wavelengths to eventually optimize the coupling efficiency of the whole system.  
         [0060]     Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made, for example replacing the bowl with a fork, without departing from the scope of the present invention which is intended to be defined by the appended claims.