Abstract:
A bi-directional transceiver, integrated module based on a silicon optical bench is provided, which comprises at least a laser diode, at least a signal detector, at least a thin film filter, at least an optical lens, an optical fiber and an SiOB. As the optical signal of specific wavelength can be reflected or inserted by thin film filter, the module has functions of a wavelength division multiplexer and a bi-direction transceiver. Furthermore, the optical lens improves the coupling efficiency between the laser diode and the optical fiber. On the other hand, a plurality of optical elements are integrated on the same SiOB. Hence, only a single optical fiber is used and optical signals of multiple wavelengths can be handled simultaneously.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the bi-directional optic transceiver module and, more particularly to a bi-directional transceiver module based on a silicon optical bench (SiOB). 
   BACKGROUND OF THE INVENTION 
   Conventional bi-directional transceiver modules with 1550/1310 nm wavelength are utilized in a communication terminal system, such as the broad-band network and the optical fiber cable TV system. An optical transmitter converts an electric signal to an optical signal for transmission, whereas an optical receiver converts the received optical signal to an electric signal. The optical transmitter module connects the modulated light or signal emitted from the front section of a laser diode to an optical fiber. The light transmitted along the optical fiber is converted back to electrical signal at the other end of the optical receiver module. 
   In general, the optical transmitter and receiver are integrated in a single packaging arrangement module, so that the module is able to simultaneously transmit and receive light signal. Most packaging arrangements are typically assembled in a metal can in that the fabrication process is complicated and expensive.  FIG. 1  of the attached drawings shows the structure of a conventional bi-directional transceiver using the “TO-can”. The bi-directional transceiver is fabricated with a metal packaging arrangement, including a TO-can laser diode  101 , a TO-can signal detector  102 , a thin film filter type wavelength division multiplexer  103 , an optical fiber  104 , and a metal housing case  107 . 
   TO-can laser diode  101  includes a ball lens to convert an electric signal to an optical emitted signal for emission, whereas TO-can signal detector  102  receives an optical signal from the other end, and converts it to an electric signal. Thin film filter type wavelength division multiplexer (WDM)  103  can selectively reflects optical signals of a specific wavelength, by adjusting the reflection angle so that the optical signals are guided to the signal detector. Output optical signal  105  is emitted from TO-can laser diode  101  through thin film filter type wavelength division multiplexer  103 , and enters optical fiber  104 . Input optical signal  106  emitted from the other end is outputted from optical fiber  104 , and reflected by thin film filter type wavelength division multiplexer  103  before entering TO-can signal detector  102 . This type of packaging arrangement has many disadvantages. For example, it is an active alignment packaging method that is time-consuming, and the external quantum efficiency may be low due to the high light coupling loss between laser diode and optical fiber. In addition, because the TO-can is assembled with mechanical components, it has a larger size. Therefore, TO-can is suitable for low-speed transmission, but not for high-speed transmission. 
     FIG. 2  shows the basic structure of another type of transceiver, a planar light circuit, including a laser diode  201  for converting electric signals into optical signals, a signal detector  202  for converting optical signals into electric signals, a wave guide  203 , and a substrate  204  for guiding optical signals to signal detector  202  and from laser diode  201  to an optical fiber. An optical transceiver is formed on a substrate to be used as a wavelength division multiplexer. However, as the structure uses only wave guide  203  for wavelength division, its ability in signal division is poor. In addition, as the coupling between laser diode  201  and wave guide  203  is difficult, both the optical loss and the fabrication cost are high. 
   To improve the poor signal division problem, a thin film filter  301  is added to wave guide  203 , as shown in  FIG. 3 . The thin film filter is to separate the lights of different wavelengths to increase the isolation, and reduce the loss. But, as the coupling loss between laser diode  201  and wave guide  203  is too large, the overall loss of this improved structure is still high. In addition, the special thin film filter is expensive, and the overall fabrication process is complicated. 
   The silicon optical bench using silicon wafer as a basis and a semiconductor fabrication process is gaining popularity in high precision component production because the technology has the advantages of low material cost, mass productivity, ease of fabrication, and high precision. The function of a wavelength division multiplexer is achieved by installing a thin film filter on a silicon optical bench. Also, by combining optical lenses and silicon optical bench with thin film filters, the goal of high coupling efficiency can be achieved, and the external quantum efficiency can be improved. 
   However, the alignment design of a silicon optical bench affects the transmission path and the loss rate of the light. Therefore, the laser diode, signal detector, thin film, optical lens, and the locations and sizes of grooves must be accurately designed and produced in order to ensure the light to follow the designed path during reflection, refraction and penetration. During the transmission, the mode of the optical field changes after the light passing optical elements; hence, the optical loss occurs. The light coupling technique is important in reducing the loss. It is, therefore, important to utilize the optical characteristics of each optical element and a high precision production process to improve the mode of optical field, and achieve high coupling efficiency to avoid high loss. 
   SUMMARY OF THE INVENTION 
   The present invention is a light coupling and alignment design based on a silicon optical bench. By combining the optical characteristics of each optical element and SiOB production technology, the present invention provides a bi-directional transceiver module that is capable of processing multiple wavelengths. The first object of the present invention is to provide a bi-directional transceiver module based on a silicon optical bench, comprising at least a laser diode, at least a signal detector, at least a thin film filter, at least an optical lens, a groove, an optical fiber, and a silicon optical bench. The present invention utilizes a silicon wafer us a substrate, and utilizes an optical fiber and grooves etched by semiconductor etching process for guiding light. The present invention does not utilize the planar light circuit fabrication process to achieve the planar light guiding. The thin film filter can selectively reflect the optical signals of a specific wavelength to the other direction, and let the rest pass. By adjusting the reflection angle, the optical signals can be reflected to a specific location. Therefore, the thin film filter can separate optical signals of different wavelengths, and the present invention can be used as a WDM. The thin film filter must be placed between the laser diode or the signal detector and the optical fiber. The optical lens and the optical fiber can be combined to improve the light coupling efficiency of the optical signal emitted from the laser diode on its transmission path. The optical lens must be placed between die laser diode and the optical fiber. The signal detector is for receiving, the optical signal of different wavelength transmitted from the other end. 
   The present invention has the functions of both an optical transmitter and an optical receiver, and uses only a single optical fiber to transmit optical signals. Therefore, the present invention is a bi-directional module. As the entire module is fabricated on a silicon wafer, and the grooves etched by semiconductor etching process is highly precise, the bi-directional transceiver module based on an SiOB can utilize a passive alignment packaging to reduce the difficulty, time, cost of fabrication as well as achieve small size and small optical loss. The present invention is suitable for high-speed transmission. 
   These and other objects, features and advantages of the invention will be apparent to those skilled in the art, from a reading of the following brief description of the drawings, the detailed description of the preferred embodiment, and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic diagram of a conventional TO-can transceiver module. 
       FIG. 2  shows a schematic diagram of a planar light circuit transceiver module. 
       FIG. 3  shows a schematic diagram of a planar light circuit transceiver module with a thin film filter added. 
       FIG. 4  shows a first embodiment of a bi-directional transceiver module based on a silicon optical bench of the present invention. 
       FIG. 5  shows the optical transmitter and output optical signal transmission in  FIG. 4 . 
       FIG. 6  shows the optical receiver and input optical signal transmission in  FIG. 4 . 
       FIG. 7  shows the transmission path of the input optical signals to signal detector in  FIG. 4 . 
       FIG. 8  shows the transmission path of the input and output optical signals in the bi-directional transceiver of  FIG. 4 . 
       FIG. 9  shows the lenses of various types and shapes according to the present invention. 
       FIG. 10  shows a perspective view of grooves of various shapes according to the present invention. 
       FIG. 11  shows a second embodiment of a bi-directional transceiver module based on an SiOB according to the present invention. 
       FIG. 12  shows a third embodiment of a bi-directional transceiver module based on an SiOB according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 4  shows a first embodiment of the present invention, comprising a laser diode  201 , a signal detector  202 , a thin film filter  301 , an optical lens  403 , a groove  406 , an optical fiber  407 , and a silicon optical bench  404 . Optical lens  403  is placed between laser diode  201  and thin film filter  301  for improving the coupling efficiency of the optical signal emitted from laser diode  201  to optical fiber  407 . Thin film filter  301  is placed between optical lens  403 , signal detector  202  and optical fiber  407  for reflecting the optical signal transmitted from optical fiber  407  to signal detector  202 . All the optical elements are integrated on silicon optical bench  404 , and utilize only a single optical fiber  407  for optical signal transmission. 
     FIG. 5  shows the optical transmitter of  FIG. 4 . The optical transmitter comprises a laser diode  201 , a thin film filter  301 , an optical lens  403 , and an optical fiber  407 . Output optical signal  505  is emitted from laser diode  201 , entering optical lens  403 , refracted by thin film filter  301 , and finally entering optical fiber  407 . 
     FIG. 6  shows the optical receiver of  FIG. 4 . The optical receiver comprises a signal detector  202 , a thin film filter  301 , and an optical fiber  407 . Input optical signal  605  is transmitted from optical fiber  407 , reflected by thin film filter  301  to signal detector  202 . Because an optical path through the reflection of thin film filter  301  is reserved for input optical signal  605  during designing the silicon optical bench  404 , the reflected input optical signal  605  will travel along reflection groove  706 , as shown in  FIG. 7 . The slant surface at the bottom of reflection groove  706  reflects input optical signal  605  to signal detector  202 , where the slant surface at the bottom of reflection groove  706  is coated with a thin film of highly reflective metal to reduce the loss. Because the reflection of input optical signal  605  is upward, the receiving surface of signal detector  202  is downward. 
     FIG. 8  shows the transmission path of output optical signal  505  and input optical signal  605 . Output optical signal  505  and input optical signal  605  share a single optical fiber  407  for transmission. This is the basic structure of a bi-directional transceiver module. The difference lies in that output optical signal  505  and input optical signal  605  have different transmission direction and different wavelength. The use of thin film filter  301  is to reflect optical signal of a specific wavelength to the other direction, and allows the other optical signal to pass. 
   For output optical signal  505 , the structure can be divided into the first part including from laser diode  201  to thin film filter  301 , and the second part including from thin film filter  301  to optical fiber  407 . The design of the structure of the first part must take into account the mode of optical field of the output optical signal  505  after its emission from laser diode  201  and passing thin film filter  301 . The design of the second part focuses on receiving the output from the first part. In other words, the emphasis is on how to reduce the loss caused by the coupling of optical fiber  407  and output optical signal  505  after its passing thin film filter  301 . As can be seen, the mode of optical field from the first part affects the coupling efficiency of the second part. Optical lens  403  can be utilized to adjust the mode of the optical field of the optical signal, in either the first or second part, or both. In the present invention, at least one optical lens  403  is utilized for improving the mode of the optical field. 
   The optical lenses can be divided into three categories: (1) flat-tip optical fiber, referring to utilizing an optical fiber and cut the tip flat, as shown in  FIG. 9 , the cut can be straight  403   a , or slanted  403   b , (2) optical fiber lens, including conic optical fiber lens  403   c , arch optical fiber lens  403   d , and thermally-diffusion expand core fiber TEC fiber)  403   e , and (3) lens, including gradient index lens (GRIN lens)  403   f , ball lens  403   g , and aspheric lens  403   h . The flat-tip optical fibers  403   a  and  403   b  are the most commonly utilized structure. The optical fiber lens refers to making the tip of an optical fiber into a lens. The TEC fiber  403   e  refers to utilizing heat to expand the core of an optical fiber. The present invention utilizes the aforementioned types of optical lenses to improve the coupling efficiency of the optical fiber and the laser diode. 
   For input optical signal  605 , the structure can also be divided into the first part including from optical fiber  407  to thin film filter  301 , and the second part including from thin film filter  301  to signal detector  202 . Because the present invention is a bi-direction transceiver module, the overall design must take into account that the same optical element may produce different effect on lights of different wavelength. Therefore, the first part and the second part of the present invention may utilize different combination of optical elements to achieve low cost, high efficiency, and ease of mass production. 
   The SiOB utilizes the semiconductor etching process for fabricating, therefore, it is highly precise in alignment and allowance for expansion. Groove  406  in the present invention is for guiding light, and it requires high precision in alignment. Using the special lattice structure of the silicon wafer and development etching technique, the precision requirement can be easily met. Groove  406  can have different shapes to meet the requirement of different optical signals, such as V-shaped groove  406   a , V-shaped with flat bottom groove  406   b , U-shaped groove  406   c , U-shaped with flat bottom groove  406   d , necktie-shaped groove  406   e , and rhombus-shaped groove  406   f.    
   In order to fully explore the high precision in alignment and allowance for expansion in an SiOB, the present invention integrates an optical transmitter, an optical receiver and other optical elements into a silicon optical bench to make a bi-directional transceiver module. Furthermore, the thin film filter is utilized to selectively reflect or pass optical signals of specific wavelength, so that it can act as a WDM. Therefore, by combining a plurality of optical transmitters, a plurality of optical receivers, and a plurality of thin film filters, the present invention can be used as a multiple wavelengths WDM, bi-directional with a single optical fiber. 
     FIG. 11  shows the second embodiment of the present invention, a bi-directional transceiver module capable of processing multiple wavelengths. Two laser diodes  2011 ,  2012 , and thin film filter  3013  are placed on a rectangular SiOB  4041 . The two diodes  2011 ,  2012  can emit two optical signals of different wavelengths. Groove  4061  and optical fiber  407  are utilized for guiding and transmitting optical signals. Three signal detectors  2021 ,  2022 ,  2023  and corresponding thin film filters  3011 ,  3012  and  3014  are utilized for receiving optical signals of three different wavelengths. The entire transceiver module utilizes five optical lenses  4031 – 4035  to adjust the mode of the optical field to improve coupling efficiency. This embodiment is able to transmit two optical signals and receive three optical signals, all of different wavelengths. 
     FIG. 12  shows the third embodiment of the present invention. By varying groove  4062 , this embodiment uses a square SiOB  4042  to meet a different application requirement. In this embodiment, a laser diode  2013  emits an optical signal, groove  4062  and optical fiber  407  are for guiding and transmitting optical signals, four signal detectors  2024 – 2027  with corresponding thin film filters  3015 – 3018  are for receiving four optical signals simultaneously, and two optical lenses  4036 ,  4037  are used to adjust the mode of the optical field and reduce coupling loss. 
   Therefore, the present invention is applicable and can be extended to place a plurality of optical transmitters and a plurality of optical receivers on a silicon optical bench. By utilizing a plurality of thin film filters of various optical characteristics, such as reflection angle, the present invention can act as a multiple wavelengths, bi-directional transceiver module with a single optical fiber. In addition, a plurality of optical lenses can be placed in the present invention to adjust the mode of the optical fields and improve the coupling efficiency. So that, the present invention is able to provide a low-cost, multi-wavelength-function, high coupling efficiency, and easy to fabricate bi-directional transceiver module. 
   While the invention has been described in connection with what is presently considered to the most practical and preferred embodiment, it is to be understood that the invention is nor to be limited to the disclosed embodiment, but, on the contrary, it should be clear to those skilled in the art tat the description of the embodiment is intended to cover various modifications and equivalent arrangement included within the spirit and scope of the appended claims.