Abstract:
An optical amplifier array is integrated with a switching matrix with a tunable filter. As a result, switching and amplification can be performed in a common hermetic package, for example, thus offering advantages associated with small footprint and low cost. The optional integration of the tunable filter, with or without the switching matrix, further allows for the monitoring of the separate optical links to ensure the proper routing of signals and/or proper spectral slotting of the various channels in each of the WDM optical signals.

Description:
RELATED APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Application No. 60/165,431, filed Nov. 15, 1999, the teachings of which are incorporated herein by this reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Today, the most common modality for optical signal amplification is the rare-earth doped fiber amplifier. These devices have good amplification characteristics and a well-understood long-term behavior. Moreover, they can be added to a fiber link via fiber splicing, which is a low insertion loss coupling technique. 
     An alternative amplification modality is the semiconductor optical amplifier (SOA). SOA systems have a number of advantages relative to the common erbium-doped amplifier scheme. SOA&#39;s are typically electrically, rather than optically, pumped. As a result, they can be more efficient and avoid the need for ancillary, expensive optical pump devices. Moreover, they are usually physically smaller than fiber amplifiers, which require a relatively long length of doped fiber. This last characteristic is especially relevant when amplification is required in larger systems offering higher levels of functionality. 
     For example, integrated switching and amplification capabilities are relevant to optical applications such as metro WDM. In such applications, the dynamic routing of individual wavelength slots or channels to form multichannel wavelength division multiplexed (WDM) optical signals is important functionality, especially if it can be provided in small, low-cost systems. 
     SUMMARY OF THE INVENTION 
     The present invention concerns an optical amplifier array that is integrated with a switching matrix. Further, in a preferred embodiment, a tunable filter is further integrated into the system. As a result, switching and amplification can be performed in a common hermetic package, for example, thus offering advantages associated with small footprint and low cost. The optional integration of the tunable filter, with or without the switching matrix, further allows for the monitoring of the separate optical links to ensure the proper routing of signals and/or proper spectral slotting of the various channels in each of the WDM optical signals. 
     In general, according to one aspect, the invention features a multi-channel semiconductor optical amplifier system. The system comprises an optical bench. A first array and second array of fibers, having endfaces, are secured relative to the optical bench. A semiconductor optical amplifier array is installed optically between the endfaces of the first array and the endfaces of the second array to provide for optical amplification of optical signals being transmitted between the two arrays. 
     In the illustrated embodiment, the optical amplifier array is implemented as separate semiconductor chips. Alternatively, multi-striped chips can be utilized providing for further integration. 
     In the preferred embodiment, an isolator is installed on the optical bench between the endfaces of the first fiber array and the semiconductor optical amplifier array. Such isolators are useful to prevent the SOA&#39;s from lasing on any back-reflected signals. 
     Typically, in the preferred embodiment, two isolator systems are used, one between the first array and the SOA&#39;s and a second between the SOA&#39;s and the second array. Collimating lenses are typically required and are installed on the optical benches to couple light, from the first fiber array, into the semiconductor optical amplifier array. 
     Preferably, to provide for WDM monitoring, a tunable filter is installed on the bench to provide for the spectral analysis or filtering of optical signals from the first array of fibers. A detector is used to then detect the filtered optical signal. Further, to allow the filter to sample any one of the beams from the first array of fibers, an array of filter optical switches is provided that selectively transmits optical signals from one of the fibers in the first array to the tunable filter. 
     In general, according to another aspect, the invention further features a multi-channel semiconductor switch system with optical amplification. This system comprises an optical bench and first, second, and third arrays of fibers, having endfaces that are secured relative to the optical bench. In one embodiment, the first array of fibers functions as an input port and the second and third arrays function as output ports. 
     In order to provide for the switching functionality, an array of optical switches is located between the first array of fibers and the second and third array of fibers. These switches allow beams emitted from the first array of fibers to be selectively coupled to either the second or third array of fibers. 
     The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
     FIG. 1 is a top plan view of the multi-channel semiconductor switch system with optical amplification according to the present invention; 
     FIG. 2 is a perspective view illustrating the details of the beam coupling into and out of the systems and the isolation and collimation components, according to the present invention; and 
     FIG. 3 is a reverse angle view showing the SOA chips, collimating optics and the array of optical port switches. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows the optical signal switching system with semiconductor optical amplification  100 , which system has been constructed according to the principles of the present invention. 
     Specifically, a first array of fibers  110  is secured to the substrate or optical bench  112  of the system  100 . In the specific implementation illustrated, the first array of fibers comprises ten separate optical fibers  114 . Each one of these fibers has an endface  116  that is secured to the bench  112  via a first fiber mounting structure  118 . In more detail, each one of the separate fibers projects through a port in the fiber mounting structure  118  such that its endface  116  is held in a fixed relationship to the optical bench  112 . In one implementation, this endface comprises a fiber lens to improve the collimation of light emitted from the respective fiber. The beams  120  that are emitted from the endfaces  116  of the fibers  114  are transmitted through a hermetic package sidewall  122  into the hermetic region  124  of the system  100 . 
     In the illustrated embodiment, the beams enter a first optical component, which is a first or input-side isolator system  126 . This isolator system prevents backreflections into the fiber endfaces but also backreflections into the subsequent SOA&#39;s to prevent lasing. 
     The beams  120  emitted from the first isolator system  126  enter a collimator lens array  128 . This collimator lens array comprises, in the preferred or current embodiment, separate discrete lenses formed using the mass transport lens process as described in, for example, U.S. Pat. No. 5,618,474, the teachings of which are incorporated herein by this reference in their entirety. These separate lenses of the lens array  128 , focus the beams  120  so that they are coupled into a semiconductor optical amplifier array  130 . 
     The optical amplifier array  130 , in one embodiment, comprises a single, multi-striped chip. In the illustrated embodiment, however, it comprises separated, singulated semiconductor optical amplifier (SOA) chips installed on a common pedestal such that they are aligned with the optical axes of the beams  120 . 
     The diverging beams emitted from the SOA array are recollimated by a second collimator array  132 . This collimator array, again, comprises separate discrete lenses, in the preferred embodiment, which convert the generally diverging beams from the chips to more collimated beams, typically having a waist. 
     The amplified optical signal beams  134  that are emitted from the SOA chips  130  first pass through an array of optical filter switches  136 . In the illustrated embodiment, these switches are aligned in a row that is parallel to a surface of the bench  112 , but extends orthogonally to the axes of the separate amplified beams  134 . Typically, in the illustrated embodiment, the individual switches of the filter switch array  136  are “rollershade” switches as described in U.S. Pat. No. 5,784,189, for example. This configuration, however, is simply the illustrated implementation. The present invention is compatible with other switch configurations. 
     The array of optical filter switches functions to divert one of the amplified beams  134  to a tunable filter  138 . In the preferred embodiment, this tunable filter  138  bandpass filters the signal with a tunable passband so that it can assess the optical power in a single optical channel slot in a WDM signal of one of the beams  134 . In one implementation, this tunable filter  138  is a MOEMS (micro optical electromechanical system) device, such as described in U.S. patent application Ser. No. 09/649,168, filed on Aug. 25, 2000, entitled Tunable Fabry-Perot Filter, by Flanders, et al., the teachings of which are incorporated herein by this reference in their entirety, although other MOEMS tunable filters, filters based on other technologies, can be used. 
     In any case, to be compatible with modern WDM channel spacings, the passband of the tunable filter is preferably less than 100 GigaHertz (GHz) to be compatible with the promulgated ITU grid. In still another embodiment, the bandwidth of the passband is less than 50 GHz to be compatible with the 50 gigahertz offset on the ITU grid. 
     A photodiode  140  detects the filtered optical signal from the tunable filter  138  to convert it to a signal that can be accessed outside the hermetic closure  122  on the bench  112  via one of the bond pads  140  in the bond pad array  142 . Further, the photodiode can be used as a feedback system to control the gain or electrical power that is provided to the individual SOA&#39;s to control WDM signal amplification. 
     In the illustrated embodiment, after being transmitted through the optical filter switch array  136 , the amplified optical signals  134  reach an optical port switch array  144 . 
     The optical port switches  144  function to divert the amplified beams  134  to either a first output port comprising a second optical fiber array  148  or a second optical port comprising a third optical fiber array  150 . 
     In the illustrated embodiment, the optical port switches comprise rollershade switches that in an unactuated or inactivated state create an open port through which the amplified beams pass to the second output port and the third array of optical fibers  150  or in an actuated state function as reflectors that divert the beams to the first output port and the second array of fibers  148 . 
     In the preferred embodiment, there is a second isolator system  152  on the path to the second output port. In another embodiment, a third isolator system, not shown, is placed between the second output port and the port switches  144 . In still another embodiment, an isolator system is located optically after the second collimator array  132  and optically before any of the switches to prevent back reflections into the SOA&#39;s. This last configuration avoids the need for duplicate isolator arrays for each output port. 
     As described previously, each of the separate fibers of the second and third fiber arrays  148 ,  150  is secured to the bench via respective fiber mounting structures  118 . These hold the endfaces  116  of the fibers so that the beams can be coupled into the fibers. In one implementation, these output fibers have fiber lenses to improve coupling efficiency. 
     FIG. 2 shows a close up of the fiber mounting structure  118  on one of the ports. Typically, the separate fibers are secured to the mounting structure, which is in turn secured to the surface of the bench  112 . In the preferred embodiment, the fiber endfaces terminate in a nonhermetically sealed portion of the bench. Specifically, the beams  120  pass through a window structure or beam feedthrough in a sidewall of the hermetic package  122 . This has an advantage in that organic and/or epoxy compounds can be used to secure the fibers  114  to the mounting structure  118  without prejudicing the operation of the active components within the hermetic package  122  via facet contamination by carbon, for example. 
     FIG. 3 is a reverse angle view showing the specifics of the semiconductor optical amplifier array  130 . Typically, the array comprises a series of separate chips  310 , which are secured to a pedestal structure  312 . Beams  120  are coupled into input facets of the chips  310  by the first collimator array  128 . The amplified beams  134  are typically diverging and are thus recollimated by the second collimator array  132 . 
     Also shown are the specifics of the filter switch array  136 . Specifically, in the specific illustrated implementation, separate roller shade structures are attached in an orthogonal fashion to the surface of the bench  124 . They function to either reflect or transmit the beams. In a reflecting configuration, one of the beams is transmitted to the tunable filter  138  and the filtered beam is then detected by the photodetector  140 . This tunable filter is used in some cases for perform a channel inventory of the WDM signal or determine the total power of the WDM signal or assess gain tilt, for example. 
     Finally, the specifics of the port switch arrays  144  are shown. Specifically, in the illustrated embodiment, these switches comprise multiple switching elements installed on a common substrate. Specifically, two separate substrates are used, each with five switch elements. These specific switch configurations function to either transmit or reflect the amplified beams such that they are coupled into either the first or second output ports. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.