Abstract:
An optical transceiver device including a modulating assembly. In contrast with conventional transceivers, the optical transceiver device uses a modulating assembly rather than a laser. The modulating assembly is located within the transceiver itself and includes first and second collimating lenses, first and second mirrors, and a p-i-n diode. An optical signal that has not yet been modulated is introduced into the modulating assembly via the first collimating lens, and is redirected toward the p-i-n diode via the first mirror. Depending on the voltage state of the diode, the light signal is either transmitted through the diode or prevented from passing, which results in modulation of the signal for data transmission. The modulated signal passes through the modulating assembly and is reflected by the second mirror toward the second collimating lens, through which it passes before exiting the transceiver.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Patent Application Ser. No. 60/426,139, filed Nov. 13, 2002, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention generally relates to optical transceivers employed in optical communications systems. More particularly, the present invention relates to an optical transceiver that incorporates a modulating component for encoding communications data onto an optical signal. 
     2. The Related Technology 
     Fiber optic technology is increasingly employed as a method by which information can be reliably transmitted via a communications network. Networks employing fiber optic technology are known as optical communications networks, and are marked by high bandwidth and reliable, high-speed data transmission. 
     Optical communications networks typically employ optical transceivers in transmitting information via the network from a transmission node to a reception node. At the transmission node, typical optical transceivers receive an electrical data signal from a network device, such as a computer, and convert the electrical data signal to a modulated digital optical data signal using a laser. Thus, production of a pulse of light by the laser can correspond to a digital “one” or “zero,” while no pulse corresponds to a “zero” or “one,” respectively, according to the configuration of the network. The modulated optical data signal produced by the laser can then be transmitted in a fiber optic cable via the optical network, such as a LAN backbone, for instance. 
     The optical data signal is transmitted to and received by a reception node of the network. Once received by the reception node, the optical data signal is fed to another optical transceiver for conversion into electrical data signals. The electrical data signals are then forwarded to a host device, such as a computer, for processing. The optical transceivers described above have both signal transmission and reception capabilities; thus, the transmitter portion of the transceiver converts an incoming electrical signal into an optical signal, whereas the receiver portion of the transceiver converts an incoming optical signal into an electrical signal. 
     The majority of components included in the optical transceiver are disposed on a printed circuit board (“PCB”). These components include a controller, which governs general operation of the transceiver, a laser driver for controlling operation of the laser in the transmitter portion, and a post-amplifier for controlling the conversion of incoming optical signals into electrical signals in the receiver portion. These components are typically configured as integrated circuits on the PCB. 
     Despite their utility, traditional laser-based transceivers are confronted by various challenges. Among these is laser chirp, which refers to the drifting of the frequency of the optical signal produced by the transceiver. Laser chirp is temperature dependent: as the laser temperature varies during operation, the frequency drift of the light signal can likewise vary. As it affects the quality of the optical signal produced by the transceiver, laser chirp can represent a significant problem to be overcome during transceiver operation. 
     To acceptably deal with the above, lasers must be designed to mitigate the effects of laser chirp and related challenges. Unfortunately, this requires that the transceiver be implemented with a variety of devices, including temperature controllers, laser bias controls, wavelength locking components, and other circuitry for adjusting transceiver components as necessary. Not only does this increase the cost of the transceiver in terms of added manufacturing steps, it also increases the complexity of the device. 
     There is therefore a need for an optical transceiver that comprises a simple design and that can provide for the reliable modulation of data onto an optical signal. It would be a further benefit to provide an optical transceiver that operates free from the effects of frequency chirp, thereby negating the need for additional control circuitry. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly summarized, embodiments of the present invention are directed to an optical transceiver device including a modulating assembly. The present transceiver stands in contrast to typical transceivers in that the lasing component is replaced by the modulating assembly. The modulating assembly is located within the transceiver itself and comprises first and second collimating lenses, first and second mirrors, and a p-i-n diode. An un-modulated optical signal is introduced into the modulating assembly via the first collimating lens, and is redirected toward the p-i-n diode via the first mirror. Depending on the voltage state of the diode, the light signal is either transmitted through the diode or prevented from passing. In this way, the light signal is modulated for data transmission. The modulated light signal that is allowed to pass through the modulating assembly is reflected by the second mirror toward the second collimating lens, through which it passes before exiting the transceiver. The receiver portion of the transceiver is unaffected by the modulating assembly, and operates in its typical manner. 
     These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  is a block diagram depicting various components comprising the present optical transceiver according to one embodiment; 
         FIG. 2  is a schematic view of several of the components of the transmitter portion of the optical transceiver of  FIG. 1 , including a p-i-n diode; 
         FIG. 3A  shows the p-i-n diode of  FIG. 2  in a first, absorptive state; 
         FIG. 3B  shows the p-i-n diode of  FIG. 2  in a second, transmissive state; and 
         FIG. 4  is a graph showing the absorption spectra for the two operational states of the p-i-n diode of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to figures wherein like structures will be provided with like reference designations. It is understood that the drawings are diagrammatic and schematic representations of presently preferred embodiments of the invention, and are not limiting of the present invention nor are they necessarily drawn to scale. 
       FIGS. 1-3B  depict various features of embodiments of the present invention, which is generally directed to an optical transceiver including a modulating assembly. The modulating assembly is used in lieu of a laser to encode data onto an optical signal for transmission via an optical communications network. In other words, the transceivers generally do not have lasers or other internal source of light, and the data is modulated onto the channels without the transceivers using internal sources of light. Instead, the transceivers use an external source of light as described herein. The channels λ are combined by a multiplexor and are transmitted to an optical communications network (not shown) for receipt by a remote device Utilization of the modulating assembly enables simplification of the transceiver design, thereby reducing the complexity and cost of the transceiver. 
     Reference is first made to  FIG. 1 , which depicts various components comprising one embodiment of the present optical transceiver, generally designated at  110 . The transceiver  110  generally includes a printed circuit board (“PCB”)  112 , a transmitter optical subassembly (“TOSA”)  114 , and a receiver optical subassembly (“ROSA”)  116 . 
     Both the TOSA  114  and the ROSA  116  are connected to a controller  118  that enables the transceiver  110  both to transmit and to receive optical signals that travel via an optical communications network (not shown). As will be explained, the controller  118  is responsible (along with other possible components not explicitly shown) for governing the operation of the TOSA  114 , and the ROSA  116 . It is appreciated that the controller  118  of the optical transceiver  110  depicted in  FIG. 1  can control additional components not explicitly mentioned here that cooperate to provide the functionality of the transceiver. 
     The ROSA  116  is utilized in the present transceiver  110  to receive incoming optical data signals from the communications network and convert them into electrical data signals that can be used by a host device (not shown) connected to the transceiver. Correspondingly, the TOSA  114  is utilized to convert electrical data signals from the host device into optical data signals for transmission via the communications network. In accordance with embodiments of the present invention, the TOSA  114  converts the electrical data signals without the use of a laser, as in typical transceivers. Rather, the TOSA  114  directly modulates the data contained in an electrical data signal onto an un-modulated optical signal. The optical signal, preferably comprising a single, discrete wavelength, is provided by a light source  120  and is modulated by the TOSA  114  to provide a modulated optical data signal that can be transmitted by the transceiver  110  to the communications network for receipt by a remote host device (not shown). One example of a light source that can be employed as light source  120  is found in U.S. Provisional Patent Application Ser. No. 60/426,116, entitled “Light Source Library for Arranging Optical Signals,” filed on Nov. 13, 2002, and which is incorporated herein by reference in its entirety. Further details concerning the operation of both the TOSA  114  and the transceiver  110  are given further below. 
     Reference is now made to  FIG. 2  in describing various details concerning the TOSA  114 . As can be seen, the TOSA  114  includes a modulating assembly  130  generally comprising a first collimator  132 , a first mirror  134 , a modulator  136 , a second mirror  138 , and a second collimator  140 . The modulating assembly  130  as will be described is utilized to provide a modulated optical data signal for use in an optical communications network. Details concerning the structure and operation of each of these components is described below. 
     A wavelength-distinct, un-modulated optical signal produced at the light source  120  is introduced into the TOSA  114  via an inlet  142 . In one embodiment, the un-modulated optical signal is transmitted to the TOSA  114  via a fiber optic cable  144  connecting the light source  120  to the TOSA. A first connector  146 , such as an LC connector, mates the fiber optic cable  144  to the TOSA  114  at the inlet  142 . 
     The first collimator  132  is arranged within the TOSA  114  to collimate the un-modulated optical signal received by the TOSA  114  via the inlet  142 . Any suitable type of collimating apparatus can be employed here, but in one embodiment the first collimator  132  comprises a collimating lens. As a result of passing through the first collimator, the un-modulated optical signal is shaped and focused as needed before proceeding on through the modulating assembly  130 . 
     After passing through the first collimator  132 , the un-modulated optical signal is directed to a first mirror  134 , which redirects the signal toward the modulator  136 . In the illustrated embodiment, the first mirror  134  is used to redirect the un-modulated optical signal at an angle of approximately 45 degrees. This configuration minimizes the space needed for the components of the modulating assembly  130 . 
     As a result of its interaction with the first mirror  134 , the un-modulated optical signal is directed to and incident upon the modulator  136 . As will be explained, the modulator  136  is utilized to modulate digital data onto the optical signal, converting it from an un-modulated optical signal to a modulated optical signal suitable for transmission via an optical communications network. Generally speaking, the modulator  136  can be selectively cycled between a powered state and an un-powered state in rapid succession so as to selectively enable the optical signal to either pass through the modulator or be absorbed thereby. This selective transmission of the optical signal through the modulator  136  creates a series of light pulses representing either a digital “one” or “zero,” depending on the configuration of the signal, which correspond to the data carried by electrical data signal. This in turn transforms the un-modulated optical signal, previously comprising a continuous stream of light waves, into a modulated, data-carrying optical signal, comprising a series of light pulses and light voids, which is now suitable for transmission via an optical communications network. Further details concerning this process are found further below. 
     After being modulated by the modulator  136 , the optical data signal is directed to the second mirror  138 , which redirects the signal at a 45-degree angle toward the second collimator  140 . The second collimator  140 , comprising in the illustrated embodiment a collimating lens, focuses and shapes the modulated optical data signal as needed before it exits the TOSA  114  via an outlet  148 . A second connector  150  disposed at the outlet  148  enables the TOSA  114  to mate to a fiber optic cable  152 . The fiber optic cable  152  then connects with an optical communications network (not shown) to enable the modulated optical data signal to be transmitted via the network to a remote reception node, as is well known. In one embodiment, the modulated optical data signal can be combined by a multiplexor, using wavelength division multiplexing techniques, with other modulated optical data signals to form a multiplexed data signal that is similarly transmitted via the network. 
     Reference is now made to  FIGS. 3A and 3B  in describing various details regarding the structure and operation of the modulator  136 . In presently preferred embodiments, the modulator  136  comprises a semiconductor-based p-i-n diode having an intrinsic semiconductor  162  interposed between a p-type semiconductor  160  and an n-type semiconductor  164 . The intrinsic semiconductor  162  in one embodiment comprises an indium-gallium-arsenide-phosphorus (“InGaAsP”) composition. Other compositions for both the intrinsic semiconductor, as well as for the p- and n-type semiconductors  160  and  164 , however, are also possible. Electrical contacts  166  are connected to the p-i-n diode to enable an electrical supply voltage V to be applied to the diode during transceiver operation. 
     In light of the above disclosure, it is appreciated that the modulator  136  can comprise other configurations with substantially the same functionality as will be described while still residing within the scope of the present invention. Moreover, one skilled in the art will also appreciate that the modulating assembly  130  can include different or additional components while still performing the functionality as discussed herein. Thus, these and other modifications to the present teachings are contemplated as comprising part of the invention. 
       FIG. 3A  shows the above-described p-i-n diode, which comprises the modulator  136 , in an absorptive first state encountered during operation of the optical transceiver  110 . As can be seen, the supply voltage V is not being supplied to the p-i-n diode in  FIG. 3A . This causes the p-i-n diode to absorb any optical signal incident upon it. An un-modulated optical signal, indicated at  168 , that is directed to the p-i-n diode from the first mirror  134  (see  FIG. 2 ), then, is absorbed by the p-i-n diode in this absorptive state and is prevented from passing through the diode to the second mirror  138 . 
     In contrast,  FIG. 3B  shows the p-i-n diode in a transmissive second state encountered during operation of the optical transceiver  110 . Here, the supply voltage V is supplied to the p-i-n diode, which causes it to transmit incident optical signals, such as the un-modulated optical signal shown at  168 , that is received from the first mirror  134  (see  FIG. 2 ). In this transparent state, then, the un-modulated optical signal  168  is allowed to pass through the p-i-n diode and proceed to the second mirror  138 , as already discussed. 
     The absorptive and transmissive states of the p-i-n diode described above in connection with  FIGS. 3A and 3B  enable the modulating assembly  130  to modulate a data signal onto the un-modulated optical signal. A digital electrical data signal received from a host device connected to the optical transceiver  110  can be relayed to the modulator  136  (composed of the p-i-n diode) by the controller  118  or other appropriate device. The p-i-n diode is then selectively energized and de-energized in rapid succession by the supply voltage V as needed in coordination with the electrical data signal. This causes the p-i-n diode to correspondingly oscillate between its absorptive and transmissive states according to the electrical data signal and the supply voltage. This in turn causes the un-modulated optical signal incident on the p-i-n diode to either be absorbed by or transmitted through the p-i-n diode, thereby creating a pulsed light data stream, or modulated optical data signal, that corresponds to the electrical data signal, wherein the light pulses represent digital “ones” or “zeroes” of the electrical data. This modulation process occurs at the high speeds that are typical of optical communications networks such that data transmission via the present optical transceiver is not hindered. 
     Reference is now made to  FIG. 4 , which shows a chart depicting absorption spectra for both the absorptive and transmissive states of the p-i-n diode that comprises the modulator  136  as described above. A first curve  170  shows the absorption spectrum for a range of wavelengths, which are positioned along the x axis when the modulator  136  is in the absorptive state. The range of wavelengths includes λ n  which represents the specific wavelength of the channel provided by the light source  120  to the TOSA  114 . Similarly, a second curve  172  depicts the absorption spectrum for the same range of wavelengths, including λ n , when the modulator  136  is energized by the supply voltage V, making the p-i-n diode transmissive to light signals. The y axis depicted in  FIG. 4  represents the amount of optical signal absorption by the modulator p-i-n diode in both the absorptive and transmissive states. The absorption spectra depicted in  FIG. 4  show that the amount of light absorption by the p-i-n diode when the supply voltage V is off is significantly higher than the absorption that occurs when the supply voltage is on. Thus, as already described in connection with  FIGS. 3A and 3B , an incident optical signal λ n  when the supply voltage V is off is substantially absorbed by the p-i-n diode. In contrast, an optical signal λ n  incident on the p-i-n diode when the supply voltage V is on is substantially transmitted through the p-i-n diode and continues unhindered through the remaining portion of the modulating assembly  130 . In this way, the un-modulated optical signal λ n  is modulated into a series of light pulses and voids as already discussed. 
       FIG. 4  further suggests that the structure and/or composition of the p-i-n diode can be modified as desired so as to provide an appropriate absorption profile for an optical signal λ n  having a specified wavelength. For example, the absorption spectra produced by the p-i-n diode can be modified by growing a lattice structure in the intrinsic semiconductor layer of the diode. Because of this, a single type of p-i-n diode can be used in various optical transceivers to modulate optical signals having a range of distinct wavelengths. For instance, in one embodiment a p-i-n diode of a particular configuration can be used to modulate optical signals having a wavelength existing anywhere within a range of approximately 40 nanometers. In this way, optical transceivers including p-i-n diodes having one of only four different configurations could be used in a CWDM or DWDM multiplexing system to modulate optical signals throughout the entire C-band, if desired. This provides added efficiency and simplicity to such systems. 
     One example where an optical transceiver as described herein can be utilized is found in U.S. Provisional Application Ser. No. 60/426,140, entitled “System for Modulating Optical Signals,” filed on Nov. 13, 2002, and which is incorporated herein by reference in its entirety. 
     The present invention provides an alternative option for producing a modulated optical signal for use in optical communications networks and the like. Moreover, the modulating assembly negates various challenges that are common with laser-based transceivers, such as laser chirp. This in turn, eliminates the need for laser temperature controls, laser bias controls, wavelength locking components, and other control components associated with lasers, thereby simplifying transceiver design and reducing the costs of manufacture. In addition, p-i-n diodes are relatively easier to manufacture and produce than are traditional lasers disposed in known optical transceivers. 
     Another advantage derived from the present invention involves the coupling of a fiber optic cable to the optical transceiver. The end of a fiber optic cable typically possesses a relatively small cross sectional optical transmission area, typically in the range of 7 microns in diameter. The cross sectional optical area of a typical laser in known optical transceivers is typically on the order of only 1×2 microns. Thus, alignment of the laser output with the end of the fiber optic cable is difficult and often results in optical coupling efficiency losses of up to 50%. In contrast, the modulating assembly of the present invention can produce a modulated optical signal having a cross sectional diameter of 50 or even 100 microns. This enables the optical output of the modulating assembly to be easily coupled with the end of the fiber optic cable, resulting in a substantially greater coupling efficiency at the TOSA/cable interface. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.