This invention provides a novel wavelength-separating-routing (WSR) apparatus that uses a diffraction grating to separate a multi-wavelength optical signal by wavelength into multiple spectral channels, which are focused onto an array of corresponding channel micromirrors. The channel micromirrors are individually controllable and continuously pivotable to reflect the spectral channels into selected output ports. As such, the inventive WSR apparatus is capable of routing the spectral channels on a channel-by-channel basis and coupling any spectral channel into any one of the output ports. The WSR apparatus of the invention may further employ a polarization diversity scheme, whereby polarization-sensitive effects become inconsequential and insertion loss is minimized. The WSR apparatus of the invention may additionally be equipped with servo-control and channel equalization capabilities. The WSR apparatus of the invention can be used to construct a novel class of dynamically reconfigurable optical add-drop multiplexers (OADMs) for WDM optical networking applications.
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19. An optical apparatus, comprising:
fiber collimators providing an input pod for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component; a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets optical beams; and
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit;
wherein said fiber collimators are arranged in a one-dimensional array.
25. A method of dynamic routing of a multi-wavelength optical signal in a polarization diversity arrangement, comprising:
adjusting an alignment of said multi-wavelength optical signal;
decomposing said multi-wavelength optical signal into first and second polarization components;
rotating a polarization of said second polarization component It) be substantially parallel to a polarization of the first polarization component;
separating said first and second polarization components by wavelength respectively into U) first and second sets of optical beams;
focusing said first and second sets of optical beams onto an array of micromirrors dynamically controlling said micromirrors to reflect said first and second sets of optical beams into selected output ports;
rotating a polarization of said reflected first set of optical beams by approximately 90-degrees; and
recombining said reflected first and second sets of optical beams by wavelength into reflected spectral channels.
20. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component; a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams;
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit; and
a beam-focuser for focusing said first and second sets of optical beams onto said channel micromirrors.
27. A method of dynamic routing of a multi-wavelength optical signal in a polarization diversity arrangement, comprising:
decomposing said multi-wavelength optical signal into first and second polarization components;
adjusting a relative alignment between said first and second polarization components;
rotating a polarization of said second polarization component to be substantially parallel to a polarization of the first polarization component;
separating said first and second polarization components by wavelength respectively into first and second sets of optical beams;
focusing said first and second sets of optical beams onto an array of micromirrors;
dynamically controlling said micromirrors to reflect said first awl second sets of optical beams into selected output pods;
rotating a polarization of said reflected first set of optical beams by approximately 90-degrees; and
recombining said reflected first and second sets of optical beams by wavelength into reflected spectral channels.
12. An optical apparatus, comprising:
fiber collimators providing an input pod for a multi-wavelength optical signal and a plurality of output pods;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams; and
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit;
wherein said polarization-displacing unit comprises a polarizing beam splitter and a first beam-deflecting unit.
21. A method of dynamic routing of a multi-wavelength optical signal in a polarization diversity arrangement comprising:
decomposing said multi-wavelength optical signal into first and second polarization components;
providing an anamorphic beam magnification to said first and second polarization components, respectively;
rotating a polarization of said second polarization component to be substantially parallel to a polarization of the first polarization component;
separating said first and second polarization components by wavelength respectively into first and second sets of optical beams;
focusing said first and second sets of optical beams onto an array of micromirrors;
dynamically controlling said micromirrors to reflect said first and second sets of optical beams into selected output ports;
rotating a polarization of said reflected first, set of optical beams of approximately 90-degrees; and
recombining said reflected first and second sets of optical beams by wavelength into reflected spectral channels.
17. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams; and
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit arid said polarization-displacing unit;
wherein each channel micromirror is pivotable about two axes; and
wherein said fiber collimators are arranged in a two-dimensional array.
18. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal arid a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams; and
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit;
wherein said array of channel micromirrors reflects said first and second sets of optical beams so as to couple said beams into selected output ports.
3. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams; and
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit;
wherein said polarization-displacing unit comprises a plurality of polarization-displacing elements in correspondence with said input port and said output ports.
23. A method of dynamic routing of a multi-wavelength optical signal in a polarization diversity arrangement, comprising:
decomposing said multi-wavelength optical signal into first and second polarization components;
rotating a polarization of said second polarization component to be substantially parallel to a polarization of the first polarization component;
separating said first, and second polarization components by wavelength respectively into first and second sets of optical beams;
focusing said first and second sets of optical beams onto an array of micromirrors;
dynamically controlling said micromirrors to reflect said first and second sets of optical beams into selected output ports;
rotating a polarization of said reflected first set of optical beams by approximately 90-degrees;
recombining said reflected first and second sets of optical beams by wavelength into reflected spectral channels
monitoring optical power levels of said reflected spectral channels coupled into said output pods; and
providing Feedback control of said micromirrors.
7. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams;
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first mid second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit; and
a beam-modifying unit for providing anamorphic beam magnification of said first and second polarization components and anamorphic beam demagnification of said reflected first and second sets of optical beams.
15. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams;
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit; and
a servo-control assembly, including a spectral monitor for monitoring optical power lever of said reflected spectral channels and a processing unit responsive to said optical power levels for controlling said channel micromirrors.
10. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams;
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit; and
an array of collimator-alignment mirrors in optical communication with said fiber collimators and said polarization-displacing unit for adjusting an alignment of said multi-wavelength optical signal from said input port and for directing said reflected spectral channels into said output ports.
1. An optical apparatus, comprising:
fiber collimators providing an input port for a multi-wavelength optical signal and a plurality of output ports;
a polarization-displacing unit that decomposes said multi-wavelength optical signal into first and second polarization components;
a polarization-rotating unit that rotates a polarization of the second polarization component to be substantially parallel to a polarization of the first polarization component;
a wavelength-separator that separates said first and second polarization components by wavelength into first and second sets of optical beams; and
an array of channel micromirrors positioned to reflect said first and second sets of optical beams such that said reflected first and second sets of optical beams are recombined by wavelength into reflected spectral channels by said polarization-rotating unit and said polarization-displacing unit;
wherein said polarization-displacing unit comprises a polarization-displacing element in optical communication with said input port and said output ports, and
wherein said polarization-rotating unit comprises a polarization-rotating element, in optical communication with said polarization-displacing element.
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This application is a continuation-in-part of U.S. patent application Ser. No. 09/938,426, filed on Aug. 23, 2001, now U.S. Pat. No. 6,625,346 and which claims priority from U.S. Provisional Patent Application Ser. No. 60/277,217, filed on Mar. 19, 2001.
This invention relates generally to optical communication systems. More specifically, it relates to a novel class of dynamically reconfigurable optical add-drop multiplexers (OADMs) for wavelength division multiplexed optical networking applications.
As fiber-optic communication networks rapidly spread into every walk of modern life, there is a growing demand for optical components and subsystems that enable the fiber-optic communications networks to be increasingly scalable, versatile, robust, and cost-effective.
Contemporary fiber-optic communications networks commonly employ wavelength division multiplexing (WDM), for it allows multiple information (or data) channels to be simultaneously transmitted on a single optical fiber by using different wavelengths and thereby significantly enhances the information bandwidth of the fiber. The prevalence of WDM technology has made optical add-drop multiplexers indispensable building blocks of modern fiber-optic communication networks. An optical add-drop multiplexer (OADM) serves to selectively remove (or drop) one or more wavelengths from a multiplicity of wavelengths on an optical fiber, hence taking away one or more data channels from the traffic stream on the fiber. It further adds one or more wavelengths back onto the fiber, thereby inserting new data channels in the same stream of traffic. As such, an OADM makes it possible to launch and retrieve multiple data channels (each characterized by a distinct wavelength) onto and from an optical fiber respectively, without disrupting the overall traffic flow along the fiber. Indeed, careful placement of the OADMs can dramatically improve an optical communication network's flexibility and robustness, while providing significant cost advantages.
Conventional OADMs in the art typically employ multiplexers/demultiplexers (e.g., waveguide grating routers or arrayed-waveguide gratings), tunable filters, optical switches, and optical circulators in a parallel or serial architecture to accomplish the add and drop functions. In the parallel architecture, as exemplified in U.S. Pat. No. 5,974,207, a demultiplexer (e.g., a waveguide grating router) first separates a multi-wavelength signal into its constituent spectral components. A wavelength switching/routing means (e.g., a combination of optical switches and optical circulators) then serves to drop selective wavelengths and add others. Finally, a multiplexer combines the remaining (i.e., the pass-through) wavelengths into an output multi-wavelength optical signal. In the serial architecture, as exemplified in U.S. Pat. No. 6,205,269, tunable filters (e.g., Bragg fiber gratings) in combination with optical circulators are used to separate the drop wavelengths from the pass-through wavelengths and subsequently launch the add channels into the pass-through path. And if multiple wavelengths are to be added and dropped, additional multiplexers and demultiplexers are required to demultiplex the drop wavelengths and multiplex the add wavelengths, respectively. Irrespective of the underlying architecture, the OADMs currently in the art are characteristically high in cost, and prone to significant optical loss accumulation. Moreover, the designs of these OADMs are such that it is inherently difficult to reconfigure them in a dynamic fashion.
U.S. Pat. No. 6,204,946 to Askyuk et al. discloses an OADM that makes use of free-space optics in a parallel construction. In this case, a multi-wavelength optical signal emerging from an input port is incident onto a ruled diffraction grating. The constituent spectral channels thus separated are then focused by a focusing lens onto a linear array of binary micromachined mirrors. Each micromirror is configured to operate between two discrete states, such that it either retroreflects its corresponding spectral channel back into the input port as a pass-through channel, or directs its spectral channel to an output port as a drop channel. As such, the pass-through signal (i.e., the combined pass-through channels) shares the same input port as the input signal. An optical circulator is therefore coupled to the input port, to provide necessary routing of these two signals. Likewise, the drop channels share the output port with the add channels. An additional optical circulator is thereby coupled to the output port, from which the drop channels exit and the add channels are introduced into the output port. The add channels are subsequently combined with the pass-through signal by way of the diffraction grating and the binary micromirrors.
Although the aforementioned OADM disclosed by Askyuk et al. has the advantage of performing wavelength separating and routing in free space and thereby incurring less optical loss, it suffers a number of limitations. First, it requires that the pass-through signal share the same port/fiber as the input signal. An optical circulator therefore has to be implemented, to provide necessary routing of these two signals. Likewise, all the add and drop channels enter and leave the OADM through the same output port, hence the need for another optical circulator. Moreover, additional means must be provided to multiplex the add channels before entering the system and to demultiplex the drop channels after exiting the system. This additional multiplexing/demultiplexing requirement adds more cost and complexity that can restrict the versatility of the OADM thus-constructed. Second, the optical circulators implemented in this OADM for various routing purposes introduce additional optical losses, which can accumulate to a substantial amount. Third, the constituent optical components must be in a precise alignment, in order for the system to achieve its intended purpose. There are, however, no provisions provided for maintaining the requisite alignment; and no mechanisms implemented for overcoming degradation in the alignment owing to environmental effects such as thermal and mechanical disturbances over the course of operation.
U.S. Pat. No. 5,906,133 to Tomlinson discloses an OADM that makes use of a design similar to that of Aksyuk et al. There are input, output, drop and add ports implemented in this case. By positioning the four ports in a specific arrangement, each micromirror (being switchable between two discrete positions) either reflects its corresponding channel (coming from the input port) to the output port, or concomitantly reflects its channel to the drop port and an incident add channel to the output port. As such, this OADM is able to perform both the add and drop functions without involving additional optical components (such as optical circulators used in the system of Aksyuk et al.). However, because a single drop port is designated for all the drop channels and a single add port is designated for all the add channels, the add channels would have to be multiplexed before entering the add port and the drop channels likewise need to be demultiplexed upon exiting from the drop port. Moreover, as in the case of Askyuk et al., there are no provisions provided for maintaining requisite optical alignment in the system, and no mechanisms implemented for combating degradation in the alignment due to environmental effects over the course of operation.
As such, the prevailing drawbacks suffered by the OADMs currently in the art are summarized as follows:
Moreover, the optical alignment is not actively maintained, rendering it susceptible to environmental effects such as thermal and mechanical disturbances over the course of operation.
In view of the foregoing, there is an urgent need in the art for optical add-drop multiplexers that overcome the aforementioned shortcomings in a simple, effective, and economical construction.
The invention provides a polarization diversity wavelength-separating-routing (WSR) apparatus and method which minimizes insertion loss and polarization-dependent loss (PDL).
In WSR apparatus with which the invention may be used, a multi-wavelength optical signal is provided from an input port to a wavelength-separator which separates the multi-wavelength optical signal by wavelength into multiple spectral channels. Each channel may be characterized by a distinct center wavelength and associated bandwidth. A beam-focuser may focus the spectral channels into corresponding spots onto a plurality of channel micromirrors positioned such that each channel micromirror receives one of the spectral channels. The channel micromirrors are individually controllable and movable, e.g., continuously pivotable or rotatable, so as to reflect the spectral channels into selected ones of the output ports. Each output port may receive any number of the reflected spectral channels.
In one aspect, the WSR apparatus of the invention employs a polarization diversity arrangement to overcome polarization-sensitive effects the constituent optical elements may possess. A polarization-displacing unit and a polarization-rotating unit may be disposed along the optical path between the fiber collimators providing the input and output ports and the wavelength-separator which separates the input multi-wavelength optical signal into the constituent wavelengths. The polarization-displacing unit decomposes the input multi-wavelength optical signal into first and second polarization components. The polarization-rotating unit may subsequently rotate the polarization of the second polarization component so that its polarization is substantially parallel to the first polarization component, e.g., by 90-degrees. The wavelength-separator separates the incident optical signals by wavelength into first and second sets of optical beams, respectively. The beam-focuser may focus the first and second sets of optical beams into corresponding focused spots, impinging onto the channel micromirrors. The first and second optical beams associated with the same wavelength may impinge onto (and be manipulated by) the same channel micromirror. The channel micromirrors may be individually controlled such that the first and second sets of optical beams are deflected, upon reflection. The reflected first set of optical beams may subsequently undergo a rotation in polarization by, e.g., 90 degrees, by the polarization-rotating unit. This enables the polarization-displacing unit to recombine the reflected first and second sets of optical beams by wavelength respectively into reflected spectral channels, prior to being coupled into the output ports.
The polarization-displacing unit may comprise one or more polarization-displacing elements, each being a birefringent beam displacer, or a polarizing-beam-splitting element, e.g., a polarizing beam splitter in conjunction with a suitable beam-reflector. The polarization-rotating unit may include one or more polarization rotating elements, each being a half-wave plate, a Faraday rotator, or a liquid crystal rotator known in the art.
A distinct feature of the channel micromirrors in the WSR apparatus is that the motion of each channel micromirror is under analog control such that its pivoting angle can be continuously adjusted. This enables each channel micromirror to scan its corresponding spectral channel across all possible output ports and thereby direct the spectral channel to any desired output port.
In the WSR apparatus, the wavelength-separator may be a ruled diffraction grating, a holographic diffraction grating, an echelle grating, a curved diffraction grating, a transmission grating, a dispersing prism, or other wavelength-separating means known in the art. The beam-focuser may be a single lens, an assembly of lenses, or other beam-focusing means known in the art. The channel micromirrors may be silicon micromachined mirrors, reflective ribbons (or membranes), or other types of beam-deflecting means known in the art. Each channel micromirror may be pivotable about one or two axes. Fiber collimators serving as the input and output ports may be arranged in a one-dimensional or two-dimensional array. In the latter case, the channel micromirrors may be pivotable biaxially.
In another aspect, the WSR apparatus of the invention may comprise an array of collimator-alignment mirrors, in optical communication with the wavelength-separator and the fiber collimators, for adjusting the alignment of the input multi-wavelength signal and for directing the spectral channels into the selected output ports by way of angular control of the collimated beams. Each collimator-alignment mirror may be rotatable about one or two axes. The collimator-alignment mirrors may be arranged in a one-dimensional or two-dimensional array. First and second arrays of imaging lenses may additionally be optically interposed between the collimator-alignment mirrors and the fiber collimators such that the collimator-alignment mirrors are effectively “imaged” onto the corresponding fiber collimators to ensure an optimal alignment.
In another aspect, the WSR apparatus of the invention may include a servo-control assembly, in communication with the channel micromirrors and the output ports. The servo-control assembly serves to monitor the optical power levels of the spectral channels coupled into the output ports and further provide control of the channel micromirrors on an individual basis, so as to maintain a predetermined coupling efficiency of each spectral channel into one of the output ports. As such, the servo-control assembly provides dynamic control of the coupling of the spectral channels into the respective output ports and actively manages the optical power levels of the spectral channels coupled into the output ports. (If the WSR apparatus includes an array of collimator-alignment mirrors as described above, the servo-control assembly may additionally provide dynamic control of the collimator-alignment mirrors.) Moreover, the utilization of such a servo-control assembly effectively relaxes the requisite fabrication tolerances and the precision of optical alignment during assembly of a SR apparatus of the invention, and further enables the system to correct for shift in optical alignment over the course of operation. A WSR apparatus incorporating a servo-control assembly thus described is termed a WSR-S apparatus, in the following discussion.
The WSR apparatus of the invention affords a variety of optical devices, including a novel class of dynamically reconfigurable optical add-drop multiplexers (OADMs), that provide many advantages over the prior art devices, notably:
In this specification and appended claims, a “spectral channel” is characterized by a distinct center wavelength and associated bandwidth. Each spectral channel may carry a unique information signal, as in WDM optical networking applications.
In operation, a multi-wavelength optical signal emerges from the input port collimator 110-1. The diffraction grating 101 angularly separates the multi-wavelength optical signal into multiple spectral channels, which are in turn focused by the focusing lens 102 into a spatial array of distinct spectral spots (not shown in
For purposes of illustration and clarity, only a select few, e.g., three, of the spectral channels, along with the input multi-wavelength optical signal, are graphically illustrated in FIG. 1A and the following figures. It should be noted, however, that there can be any number of the spectral channels in a WSR apparatus of the invention (so long as the number of spectral channels does not exceed the number of channel mirrors employed in the system). It should also be noted that the optical beams representing the spectral channels shown in FIG. 1A and the following figures are provided for illustrative purpose only. That is, their sizes and shapes may not be drawn according to scale. For instance, the input beam and the corresponding diffracted beams generally have different cross-sectional shapes, so long as the angle of incidence upon the diffraction grating is not equal to the angle of diffraction, as is known to those skilled in the art.
In the embodiment of
The corresponding spectral channels diffracted from the diffraction grating 101 are generally elliptical in cross-section; they may be of the same size as the input beam in one dimension and elongated in the other dimension.
It is known that the diffraction efficiency of a diffraction grating is generally polarization-dependent. That is, the diffraction efficiency of a grating in a standard mounting configuration may be considerably higher for P-polarization that is perpendicular to the groove lines on the grating than for S-polarization that is orthogonal to P-polarization, especially as the number of groove lines (per unit length) increases. To mitigate such polarization-sensitive effects, a quarter-wave plate 104 may be optically interposed between the diffraction grating 101 and the channel micromirrors 103, and preferably placed between the diffraction grating 101 and the focusing lens 102 as is shown in FIG. 1A. In this way, each spectral channel experiences a total of approximately 90-degree rotation in polarization upon traversing the quarter-wave plate 104 twice. (That is, if a beam of light has P-polarization when first encountering the diffraction grating, it would have predominantly (if not all) S-polarization upon the second encountering, and vice versa.) This ensures that all the spectral channels incur nearly the same amount of round-trip polarization dependent loss.
In the WSR apparatus 100 of
As described above, a unique feature of the invention is that the motion of each channel micromirror is individually and continuously controllable, such that its position, e.g., pivoting angle, can be continuously adjusted. This enables each channel micromirror to scan its corresponding spectral channel across all possible output ports and thereby direct the spectral channel to any desired output port. To illustrate this capability,
A WSR apparatus embodying the invention may further comprise an array of collimator-alignment mirrors, for adjusting the alignment of the input multi-wavelength optical signal and facilitating the coupling of the spectral channels into the respective output ports, as shown in
The embodiment of
In addition to facilitating the coupling of the spectral channels into the respective output ports as described above, the collimator-alignment mirrors in the above embodiments also serve to compensate for misalignment, e.g., due to fabrication and assembly errors, in the fiber collimators that provide for the input and output ports. For instance, relative misalignment between the fiber cores and their respective collimating lenses in the fiber collimators can lead to pointing errors in the collimated beams, which may be corrected for by the collimator-alignment mirrors. For these reasons, the collimator-alignment mirrors are preferably rotatable about two axes. They may be silicon micromachined mirrors, for fast rotational speeds. They may also be other types of mirrors or beam-deflecting elements known in the art.
To optimize the coupling of the spectral channels into the output ports and further maintain the optimal optical alignment against environmental effects such as temperature variations and mechanical instabilities over the course of operation, a WSR apparatus of the invention may incorporate a servo-control assembly, for providing dynamic control of the coupling of the spectral channels into the respective output ports on a channel-by-channel basis. A WSR apparatus incorporating a servo-control assembly is termed a WSR-S apparatus within this specification.
In the embodiment of
The incorporation of a servo-control assembly provides additional advantages of effectively relaxing the requisite fabrication tolerances and the precision of optical alignment during initial assembly of a WSR apparatus of the invention, and further enabling the system to correct for shift in the alignment over the course of operation. By maintaining an optimal optical alignment, the optical losses incurred by the spectral channels are also significantly reduced. As such, the WSR-S apparatus thus constructed is simpler and more adaptable in structure, more robust in performance, and lower in cost and optical loss. Accordingly, the WSR-S (or WSR) apparatus of the invention may be used to construct a variety of optical devices and utilized in many applications. Moreover, a novel class of optical add-drop multiplexers (OADMs) may be built upon the WSR-S (or WSR) apparatus of the invention, as exemplified in the following embodiments.
In the above embodiment, the optical combiner 550 may be a K×1 (K≧2) broadband fiber-optic coupler, wherein there are K input-ends and one output-end. The pass-through spectral channels and the add spectral channels are fed into the K input-ends, e.g., in a one-to-one correspondence, and the combined optical signal exits from the output-end of the K×1 fiber-optic coupler as the output multi-wavelength optical signal of the system. Such a multiple-input coupler also serves the purpose of multiplexing a multiplicity of add spectral channels to be coupled into the OADM 500. If the optical power levels of the spectral channels in the output multi-wavelength optical signal are desired to be actively managed, such as being equalized at a predetermined value, two spectral monitors may be utilized. As a way of example, the first spectral monitor may receive optical signals tapped off from the pass-through port 530 and the drop ports 540-1 through 540-N, e.g., by way of fiber-optic couplers as depicted in
In the embodiment of
As discussed above, the diffraction efficiency of a diffraction grating is polarization-sensitive, and such polarization-sensitive effects may give rise to significant insertion loss and polarization-dependent loss (PDL) in an optical system. The situation is further exacerbated in WDM optical networking applications, where the polarization state of WDM signals is typically indeterminate and may vary with time. This can produce an undesirable time-varying insertion loss that may cause the optical signals to fall below acceptable levels or render them unusable. Thus, it is desirable to avoid such polarization-sensitive effects, and the invention affords a polarization diversity scheme that addresses this, as will now be described.
The first and second polarization components (optical signals 722, 732) emerging from the polarization-displacing unit 720 and the polarization-rotating unit 730, respectively, may undergo an unamorphic beam magnification by a beam-modifying unit 740 and emerge as spatially separated and magnified beams 742, 744 which impinge upon the diffraction grating 101. The configuration may be such that the beam-modifying unit 740 preferentially enlarges the beam size in the direction perpendicular to the groove lines on the diffraction grating 101. This magnifies the optical beams in a direction perpendicular to the groove lines of the grating so that the focused beams produced by the focusing lens 102 are narrower in this direction, i.e., perpendicular to the groove lines. This enables use, for example, of rectangular shaped micromirrors. The diffraction grating 101 subsequently separates the magnified first and second polarization components 742, 744 by wavelength into first and second sets of diffracted optical beams. Each set of optical beams comprises multiple wavelengths λ1 through λM, which are diffracted by the diffraction grating 101 at different angles. The focusing lens 102 in turn focuses the diffracted optical beams into corresponding focused spots which impinge onto the channel micromirrors 103. Each focused spot may be elliptical in cross-section. Further, the first and second diffracted optical beams having the same wavelength, e.g., λi, are arranged to impinge onto the same channel micromirror, e.g., the channel micromirror 103-i, see FIG. 7B. In this way, each channel micromirror handles concurrently two optical beams having the same polarization and wavelength.
Referring to
It should be appreciated that the rotation in polarization produced by a polarization-rotating element, e.g., the polarization-rotating unit 730, may have slight variations about a prescribed angle, e.g., 90-degrees, due to imperfections that may exist in a practical system. Such variations, however, will not significantly affect the overall performance of the invention.
In the embodiment of
Those skilled in the art will appreciate that rather than using a birefringent beam displacer, the polarization-displacing element 720A may alternatively be provided by a suitable polarizing-beam-splitting element, e.g., a polarizing beam splitter commonly used in the art along with an appropriate beam-deflector or prism (such that the two emerging polarization components propagate in parallel). Such a polarizing-beam-splitting element provides a substantially similar function to the aforementioned birefringent beam displacer. In general, a polarization-displacing element in the invention may be embodied by any optical element that provides a dual function of polarization separating and combining, as depicted in FIG. 7C.
Likewise, the polarization-rotating unit 730 may comprise a single polarization-rotating element, e.g., a half-wave plate, a liquid crystal rotator, a Faraday rotator, or any other means known in the art that is capable of rotating the polarization of an optical beam by a prescribed angle, e.g., 90 degrees.
Alternatively, the polarization-displacing unit 720 may comprise a plurality of polarization-displacing elements, each corresponding to one or more fiber collimators 110 in the embodiment of
Those skilled in the art will appreciate that the exemplary embodiments of
Moreover, the beam-modifying unit 740 may comprise an assembly of cylindrical lenses or prisms, in optical communication with the polarization-displacing unit 720 along with the polarization-rotating unit 730 and the diffraction grating 101. In general, a beam-modifying unit may be embodied by any optical structure that is capable of magnifying the input optical signal and de-magnifying the reflected optical beams according to a predetermined ratio. Such a beam-modifying unit may be particularly useful in applications that call for a refined spectral resolution, such as DWDM optical networking applications.
The WSR apparatus 700 of
Those skilled in the art will appreciate that the WSR apparatus 700 of
In the embodiment of
In the embodiment of
The WSR apparatus 700 (or any one of the embodiments of
Furthermore, a dynamically reconfigurable OADM may be built upon the WSR apparatus 700, 800A, 800B or 800C (along with an associated servo-control assembly), e.g., in a manner similar to that described with respect to
Those skilled in the art will recognize that the aforementioned embodiments are provided by way of example to illustrate the general principles of the invention. Various changes, substitutions, and alternations can be made without departing from the principles and the scope of the invention as defined in the appended claims.
Wilde, Jeffrey P., Davis, Joseph E., Garrett, Mark H., Polynkin, Pavel G., Mansuripur, Masud
| Patent | Priority | Assignee | Title |
| 8611742, | Mar 15 2011 | CAPELLA PHOTONICS, INC | Wavelength switch system using angle multiplexing optics |
| RE47905, | Mar 19 2001 | Capella Photonics, Inc. | Reconfigurable optical add-drop multiplexers with servo control and dynamic spectral power management capabilities |
| RE47906, | Mar 19 2001 | Capella Photonics, Inc. | Reconfigurable optical add-drop multiplexers with servo control and dynamic spectral power management capabilities |
| Patent | Priority | Assignee | Title |
| 5629790, | Oct 18 1993 | RPX CLEARINGHOUSE LLC | Micromachined torsional scanner |
| 5868480, | Dec 17 1996 | Duke University | Image projection apparatus for producing an image supplied by parallel transmitted colored light |
| 5960133, | Jan 27 1998 | Tellium, INC | Wavelength-selective optical add/drop using tilting micro-mirrors |
| 5974207, | Dec 23 1997 | RPX Corporation | Article comprising a wavelength-selective add-drop multiplexer |
| 6172777, | Sep 23 1997 | AIR FORCE, UNITED STATES OF AMERICA | Optical interconnection for holographic memories and method for using the same |
| 6193376, | Feb 27 1998 | Minolta Co., Ltd. | Display apparatus |
| 6204946, | Aug 21 1997 | AVAGO TECHNOLOGIES GENERAL IP SINGAPORE PTE LTD | Reconfigurable wavelength division multiplex add/drop device using micromirrors |
| 6205269, | Apr 06 1999 | Ciena Corporation | Optical add/drop multiplexer |
| 6263135, | Dec 13 1997 | AUXORA, INC | Wavelength division multiplexing/demultiplexing devices using high index of refraction crystalline lenses |
| 6289155, | Dec 13 1997 | AUXORA, INC | Wavelength division multiplexing/demultiplexing devices using dual high index of refraction crystalline lenses |
| 6343862, | Nov 20 1998 | MINOLTA CO , LTD | Projecting image display device |
| 6418250, | Feb 28 2000 | II-VI Incorporated | Apparatus and method of making a blockless optical multiplexing device |
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