Abstract:
A chip for integrating functions performed by micro-optics and RF circuits including at least one optical function module that receives an optical signal and performs at least one of a plurality of optical functions. A RF function module that receives a RF signal and perform at least one of a plurality of RF functions. The at least one optical function module and the RF function module provides a monolithic integration of optics and RF circuits on the chip.

Description:
PRIORITY INFORMATION  
       [0001]    This application claims priority from provisional application Ser. No. 60/300,296 filed Jun. 22, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to the field of communications, and in particular to the monolithic integration of planar lightwave circuits or integrated optics RF circuits.  
           [0003]    There are currently several modes of communication that are in use. Wireless and optical communications are two of the newer forms of communication and have been pursued in separate fields. There have been several attempts to combine these two forms of communications at the chip level. One of these attempts is the use of fiber to the home (FTTH) optical communications, which provides enormous bandwidth, but has a large overhead. However, it is a fixed line and does not meet the necessary requirements for wireless applications. Another is the radio frequency (RF) approach, which can provide the convenience of wireless but it is bandwidth limited.  
           [0004]    There is a need in the art to combine these two modes of communications so that RF monolithic microwave circuits (MMICs) and discrete optics components can be integrated to form a bridge between RF and fiber optic communication technologies.  
         SUMMARY OF THE INVENTION  
         [0005]    According to one aspect of the invention, there is provided a chip for integrating functions performed by micro-optics and RF circuits. The chip includes one or more optical function modules for assembling a plurality of optical functions. The one or more optical function modules receive an optical signal, and perform at least one of the plurality of optical functions. A RF function module assembles a plurality of RF functions. The RF function module receives a RF signal, and performs at least one of the plurality of RF functions. The one or more optical function modules and the RF function module provide a monolithic integration of optics and RF circuits on the chip.  
           [0006]    According to another aspect of the invention, there is provided a hybrid circuit including micro-optics and RF circuits. The hybrid circuit includes at least one optical function module that receives or transmits an optical signal and performs at least one of a plurality of optical functions. A RF function module that receives a RF signal and perform at least one of a plurality of RF functions. The at least one optical function module and the RF function module are integrated on a single microchip. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic block diagram of a planar chip for implementing the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    [0008]FIG. 1 is a schematic block diagram of a planar chip  2  for implementing the invention. The planar chip includes a first external optical fiber  4 . The first external optical fiber  4  receives an optical signal, and provides the optical signal to the planar chip  2  as input. Given the structural arrangement of optical fibers, the first external optical waveguide  4  has a mode size of approximately 8-10 μm. The mode size can vary depending on the specific carrier properties of the optical signal used in the optical fiber. The first external optical fiber  4  connects the planar chip  2  to optical signals received externally. In other embodiments, there can be more than one input optical fiber to the planar chip  2 . Also, the one or more optical fibers can act as output fibers or simultaneously act as both input and output fibers in other embodiments.  
         [0009]    The optical signals that are received by the first external optical fiber  4  are provided to a first waveguide mode converter module  6 , within the planar chip  2 . The first waveguide mode converter module  6  is designed monolithically on the chip  2 , and converts the mode size of the optical signal to less than 3 μm. Also, the first waveguide mode converter module  6  is connected to one or more high index waveguides  30 . The high index waveguides  30  provide a channel for propagating the optical signals to the various modules  6 ,  8 , and  10  within the interior of the planar chip  2  without incorporating any substantial lost to the optical signal.  
         [0010]    The more waveguide structures that are used in the high index difference waveguides  30 , the higher the density of optical functions, because the optical functions and their associated optical routing scale inversely in size with respect to index contrast. However, care must be taken to ensure that loss is kept at a minimum. The high index waveguides  30  can include waveguide structures that are made from different high index materials, and the indexes can vary for each waveguide structure. Also, the high index waveguides  30  interconnect the first waveguide mode converter module  6  to a first optical function module  8 .  
         [0011]    The first optical function module  8  receives an optical signal from a first set of the high index waveguides  30  as input, and also receives a control electronic signal from a control module  32  as input. The first optical function module  8  is an integration of more than one optical function connected with one or more optical waveguides. This includes, but is not limited to, optical components, such as filters, splitters, dispersion compensation components, resonators, fiber couplers, switches, polarization rotators, frequency mux/demux, or the like. The electronic signal input is used to actuate the optical functions to be performed by the first optical function module  8 . In other embodiments, the first function module  30  can perform various optical functions simultaneously without incurring substantial loss to the performance of the planar chip  2 . After performing its optical functions, the first function module  30  provides its output to a second set of the high index waveguides  30 .  
         [0012]    The second set of the high index waveguides  30  propagates this output to a first optical-RF transducer  10 . The optical-RF transducer  10  receives the output optical signal from the first optical function module  8 , and proceeds to convert the optical signal into a RF signal. The RF signal has substantially the same properties as its optical counterpart, except that the frequency of the optical signal is in the RF range, and will have the same characteristics of microwave signals. Also, the RF signal is decoupled from its optical counterpart, but includes the optical function properties performed on its optical signal counterpart by the first optical function module  8 .  
         [0013]    The optical-RF transducer  10  outputs the RF signal to a first RF waveguide  36 . The RF waveguide  36  propagates the RF signal to a RF function module  12 , and is designed specifically to incorporate minimal loss to the RF signal. The dimensions of the RF waveguide  12  can vary depending on the distance between the optical-RF transducer  10  and the RF function module  12 , and the area of the planar chip  2 .  
         [0014]    The RF function module  12  receives as input the optical signal propagated by the RF waveguide  36 , and an electronic control signal from the control module  32  to actuate the RF function module  12 . Also, the RF function module  12  is an integration of more than one RF f unction connected with one or more RF waveguides. This includes, but is not limited to, RF components, such as filters, splitters, dispersion components, resonators, fiber couplers, switches, RF amplifiers, transistors, antennae, and frequency mux/demux. Examples of RF functions that are performed by the RF function module  12  include but are not limited to detectors, lasers, modulators, WDM mux/demux, attenuators, and gain elements.  
         [0015]    Alternatively, a RF signal can be coupled onto the planar chip  2  using RF waveguides  40  and  42 . This allows the planar chip  2  to receive both RF and optical signals. The dimensions of the RF waveguides  40  and  42  are dependent on the distance between the RF function module  12  and input ports  22  and  24 , and the area of the planar chip  2 . The larger the distance between the input ports  22  and  24 , the higher the risk of having substantial loss in an input RF signal. Therefore, the RF waveguides  40  and  42  are formed with materials, which minimize loss over long distances, and each of the RF waveguides  40  and  42  can be different from one another. In other embodiments, the distance between the RF function module  12  and input ports  22  and  24  can vary, thus requiring different types of waveguides to be used to minimize loss.  
         [0016]    Also, the RF waveguides  40  and  42  can be used as output channels for RF signals, which are processed by the RF function module  12 . In this embodiment, the ports  22  and  24  become output ports. The invention can allow the planar chip  2  to receive both optical signals and RF signals simultaneously for processing, where the ports  22  and  24  can be both input and output ports simultaneously also.  
         [0017]    When a RF signal is provided as input to ports  22  or  24 , the RF function module  12  performs its RF functions, and provides its output to a RF waveguide  38 . The RF waveguide  38  is similar to the RF waveguide  36 , and propagates the output RF signal of the RF function module  12  to a RF-optical transducer  14 . Also, the RF waveguide  38  is designed specifically to minimize loss to the output RF signal. The dimensions of the RF waveguide  38  can vary depending on the distance between the RF-optical transducer  14  and RF function module  12 , and the area of the planar chip  2 .  
         [0018]    The RF-optical transducer  14  receives the output optical signal from the RF function module  12 , and proceeds to convert the signal into an optical signal. The optical signal has substantially the same signal properties as its RF counterpart, except that the frequency of the RF signal is in the optical range. The optical signal is decoupled from its RF signal counterpart, but includes RF function properties performed on its RF signal counterpart by the RF function module  8 . The RF-optical transducer  14  provides its output to high index waveguides  34 .  
         [0019]    The high index waveguides  34  are similar to the high index waveguides  30 , and they provide a channel for propagating optical signals to modules  16  and  18  within the interior of the planar chip  2  without incorporating any substantial lost to the optical signal. As similarly described for the high index waveguides  30 , the more waveguide structures that are used in the high index difference waveguides  34 , the higher the density of optical functions, because loss is kept at a minimum. The high index waveguides  34  can also include waveguide structures that are made from different high index materials, and the indexes can vary for each waveguide structure. The high index waveguides  34  interconnect the RF-optical transducer  14  to a second optical function module  16 .  
         [0020]    The second optical function module  16  receives an optical signal associated with the output of the second optical function module  14  from a first set of the high index waveguides  34  as input, and also receives a control electronic signal from a control module  32  as input. The second optical function module  16  is an integration of more than one optical function connected with one or more optical waveguides, such as filters, splitters, dispersion compensation components, resonators, fiber couplers, switches, polarization rotators, frequency mux/demux, or the like. Examples of optical functions that are performed by the second optical function module  16  include but are not limited to detectors, lasers, modulators, WDM, mux/demux, attenuators, and gain elements. The electronic signal input is used to actuate the optical functions to be performed by the second optical function module  16 .  
         [0021]    In other embodiments, the second optical function module  16  can perform various optical functions simultaneously without incurring substantial loss to the performance of the planar chip  2 , and provides its output to a second set of the high index waveguides  34 .  
         [0022]    A second waveguide mode converter module  18  receives as input from the second set of the high index waveguides  34  the output from the second optical function module  16 , and proceeds to convert the mode of its input optical signal. In particular, the second waveguide mode converter module  18  converts a mode of an optical signal to be useable in a fiber optic line. In this case, an optical signal is converted from a mode that is less than 2 μm to a mode that is greater than 3 μm. Most fiber optic lines require modes between 8 and 10 μm. Therefore, the second waveguide mode converter  18  converts the mode of an optical signal within the range that is used in conventional fiber optic lines.  
         [0023]    The second waveguide mode converter  18  provides its output to a second external output optical fiber  20 . The second external optical fiber  20  receives the converted optical signal. Given the structural requirements of an optical fiber, the second external output optical fiber  20  has a mode size of approximately 8-10 μm. The mode size can vary depending on the specific carrier properties of an optical fiber. The second external output optical fiber  20  outputs optical signals associated with RF processing. There can be more than one output optical fiber to the planar chip  2 .  
         [0024]    The optical fibers  4  and  20  can be used as either input or output fibers simultaneously. In this embodiment, the optical fibers  4  and  20  have diameters of approximately 10 μm, however, this can vary. Also, optical fibers with mode sizes ranging from 4-50 μm can also be used in accordance with the invention.  
         [0025]    The control module  32  receives as input from an input port  26  external control signals from a controller to manage the modules  8 ,  12 , and  16 . Also, the control module  32  processes the signals from the controller into a format useable by the modules,  8 ,  12 , and  16 , and outputs interior control signals to modules  8 ,  12 , and  16 . These interior control signals include information regarding which type of functions these modules  8 ,  12 , and  16  will perform, and selective data to be provided by the modules  8   12 , and  16  to the controller. When the control module  32  receives this data, it immediately processes the information into a format useable by the controller and outputs this information through output port  28  to the controller. Also, the control module  32  can be used to monitor the workload of the modules  8 ,  12 , and  16 , therefore improving the throughput of information going in and out of the planar chip  2 . The control module  32  uses a line  44  to receive and output information to the optical module  8 ,  12 , and  16 , respectively.  
         [0026]    The invention allows the optical module  8  and  16  and RF module  12  to communicate in a unidirectional or bi-directional fashion without limiting the performance of the system  2 . For example, optical module  16  can provide its output to the mode converter module  18  and RF module  12  using the line  44 . The same occurs for modules  8  and  12 , respectively. The line  44  interconnects the optical modules  8  and  16  and RF module  12  to each other, and allows unidirectional and bi-directional communication to occur between the modules  8 ,  12 , and  16 , respectively.  
         [0027]    The planar chip  2  uses silicon mixed technology integrated with a CMOS compatible high index waveguide. In this technology, RF mixed signal (digital and analog) integrated circuits are made using standard silicon CMOS processes on a silicon substrate. Detectors can also be integrated with these components. Depending on the wavelength, silicon, germanium, or germanium detectors can be used in accordance with the invention. Integrated optic wavelength technology using one or a combination of silicon CMOS compatible materials can also be fabricated on this substrate.  
         [0028]    A designer of such monolithically integrated optical and RF mixed signal circuit has several options in a choosing a wafer substrate, a wavelength of operation, waveguide and detector materials, and waveguide forming techniques. The choice of the substrate is determined largely by cost vs. performance trade-offs. The RF devices made on compound semiconductor materials can operate at much higher frequencies, while devices made on silicon have as a general rule much lower cost. Using silicon also has the added advantage of being able to leverage off existing silicon foundries. The choice of wavelength depends on the wavelength of the optical carrier. This wavelength determines the material choice for the waveguide and the detector. The choice between growth, deposition, or wafer bonding to form a waveguide layer is based on a cost vs. performance tradeoff. Wafer bonding usually allows greater flexibility in design, since compound semiconductor wafers can be bonded to silicon wafers, whereas growth is cheaper.  
         [0029]    The invention can be used with in RADAR or electronic warfare applications. Full-systems or even sub-systems on a chip can be achieved with such technology. Also, the invention can be used in fiber optics communication systems as well as in high speed computing applications. This technology can be made relatively cheap and will provide the user with an enormous amount of bandwidth coupled with the convenience of wireless RF. RF and optical transducers and processors will seamlessly mate the RF and optics technologies together. The invention further provides low loss, low cross talk, and low EMI susceptibility. Also, electronic CMOS integrated circuits can be added for more functionality without substantially burdening the designer.  
         [0030]    Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.