WO2001057570A1

WO2001057570A1 - Segmented thin film add/drop switch and multiplexer

Info

Publication number: WO2001057570A1
Application number: PCT/US2001/003871
Authority: WO
Inventors: Guillaume C. L. Boisset; J. Michael Harris; Mark F. Krol; Qi Wu; Xingkun Wu
Original assignee: Corning Incorporated
Priority date: 2000-02-07
Filing date: 2001-02-06
Publication date: 2001-08-09
Also published as: WO2001057570A9; AU2001238045A1

Abstract

An optical switch and WADM uses a channel selector (10) to provide channel selection and reconfigurable operation. The channel selector includes a segmented filter portion (100) and a highly reflecting mirror (110). The channel selectors can be cascaded to form an N-wavelength channel WDM system. The WADM allows for selection of a wavelength channel from a multitude of channels by moving the appropriate channel selector into the path of the light beam.

Description

SEGMENTED THIN FILM ADD/DROP SWITCH AND MULTIPLEXER

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of priority under 35 U.S.C. § 120 for U.S. Patent Application Serial No. 09/466,319 filed on December 17, 1999, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates generally to optical switches, and particularly to an optical switch using thin film filters.

2. Technical Background

Wavelength Add/Drop Multiplexers (WADMs) are currently gaining considerable attention in the development of communication systems because of the flexibility, capacity, and transparency they provide. WADMs allow service providers to efficiently reconfigure networks to meet changing service requirements. This is especially helpful in metropolitan area applications because it provides the capability of adding and dropping communication payloads at each node in the communication ring. WADMs also provide the same capability for long-distance applications. At any local node, wavelength channels that are destined for the local node are directed into a drop port and integrated with local traffic. Other wavelength channels which are merely passing through the node remain undisturbed. Thus, switching is performed in the optical domain, and the inefficiencies associated with optical to electrical domain conversion are avoided.

In order to exploit the full capability of optical domain switching, WADMs must be reconfigurable and wavelength channel selectable. These two attributes enable service providers to allocate bandwidth on demand and redistribute wavelengths where required in an optical network. Most current technologies allow an add/drop node to be reconfigured; however, only a few provide full reconfigurability and channel selectability without interrupting adjacent channels.

There are several issues that need to be addressed before the capacity of WDM systems can be increased. Obviously, the ability to use more of the available spectrum is one way to increase capacity. One way to accomplish this is by increasing the number of wavelength channels in the system by reducing the spacing between channels. However, this problem is compounded by the need for broad band channels that carry more information. It has been proposed to increase the flexibility of the channel shape by differentially heating a fiber Bragg grating from one end to another. This allowed the grating to be chirped, expanding its reflected spectrum. By controlling the absolute temperature, the shape of the center of the channel could be manipulated. While this flexibility is impressive, it has a major drawback. It requires significant monitoring and control functionality to be added to the component to make it useful. Additionally, this device is an 'analog' type device. It will have a tendency to drift with time and temperature.

This points out a need for a WDM switch that flexibly selects individual wavelength channels in a system, whereby wavelength channels are flexibly allocated within the communications system.

SUMMARY OF THE INVENTION

The WDM switch and WADM of the present invention provides flexible selection and allocation of wavelength channels with a WDM communications system. The switch and WADM use a channel selector for wavelength channel selection. The channel selector is composed of multiple single channel filter elements and a highly reflecting mirror that covers the wavelength range of interest. The channel selector also provides the ability to band pass filter the optical signal. The band pass filter can be selected for either wide band or narrow band operation depending on the requirements of channel spacing. One aspect of the present invention is an optical device for directing a light signal having a plurality of wavelength channels. The optical device includes: a wavelength selecting filter that transmits a selected wavelength channel and reflects non-selected wavelength channels, wherein the wavelength selecting filter causes the reflected non-selected wavelength channels to have a first phase shift; and a reflector disposed on a portion of the wavelength selecting filter, the reflector having a reflector thickness that is selected to cause a reflected light signal to have a second phase shift that is substantially equal to an integer multiple of 2π times the first phase shift.

Another aspect of the invention is an optical device for directing a light signal having a plurality of wavelength channels, the optical device including an input port, a plurality of drop ports, and an output port. The optical device also includes a plurality of channel selectors coupled to the input port, the plurality of drop ports, and the output port, wherein each channel selector selectively transmits a wavelength channel into a corresponding drop port. A plurality of flexure arms are included, each of the flexure arms having a chuck disposed at a first end for holding a corresponding channel selector, and a pivoting member at a second end, whereby the flexure arm is rotatable around an axis of rotation to move the channel selector in a plane of rotation between a first position and a second position. An optical plate having an axial support member is connected to each of the pivoting members at the axis of rotation, whereby the axial support member is adjustable to align the plurality of flexure arms such that their planes of rotation are substantially parallel.

Another aspect of the invention is a method of fabricating an optical device. The method including the steps of: providing a wavelength selective filter that transmits light having a predetermined spectral pass band and reflects light outside the predetermined spectral pass band, whereby the wavelength selective filter causes filter- reflected light to have a first phase shift; and disposing a reflector on a portion of the wavelength selecting filter, the reflector having a reflector thickness that is selected to cause reflector-reflected light to have a second phase shift that is substantially equal to an integer multiple of 2π times the first phase shift.

Another aspect of the invention is a method of fabricating an optical device for directing a light signal having a plurality of wavelength channels. The method includes providing a chuck assembly that includes a plurality of flexure arms each having a chuck disposed at a first end, a flexure member, and a pivoting member disposed at a second end, and an optical plate having an axial support member, whereby each of the pivoting members is connected to the axial support member and rotatable around an axis of rotation in a plane of rotation. A channel selector is attached to each chuck, each of the channel selectors including a reflector disposed on a wavelength selective filter, whereby the wavelength selective filter transmits one wavelength channel and the reflector reflects all of the wavelength channels. Each of the flexure members is adjusted to cause a light incident side of each channel selector to be parallel to its respective plane of rotation. The axial support member is adjusted to thereby align the plurality of flexure arms such that their planes of rotation are substantially parallel.

Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

-Figure 1 is a diagram of the segmented channel selector according to a first embodiment;

Figure 2 is a diagram of the segmented channel selector according to a first embodiment showing channel selection;

Figure 3 is a linearly variable channel selector according to a second embodiment;

Figure 4 is a diagram of a channel selector having a bandpass filter in accordance with a third embodiment; Figure 5 is a diagram of a channel selector and bandpass filter in accordance with a fourth embodiment ;

Figure 6 is a method of manufacturing a thin film channel selector; Figure 7 is an alternate method of manufacturing a thin film channel selector; Figure 8 A is a top view of a channel selector and wavelength selective filter according to a fifth embodiment of the present invention;

Figure 8B is a side view of the channel selector shown in Figure 8 A; Figure 9A is a top view of a channel selector and segmented wavelength selective filter according to a sixth embodiment of the present invention;

Figure 9B is a side view of the channel selector shown in Figure 9A; Figure 9C is a side view of the channel selector shown in Figure 9A;

Figure 10 is a plan view of a switch incorporating the channel selectors disclosed in the fourth and fifth embodiments of the present invention;

Figure 11 is a plan view of an Add/Drop switch incorporating the channel selectors disclosed in the fourth and fifth embodiments of the present invention; Figure 12 is a diagram of an WADM switch using the channel selectors of the fourth and fifth embodiment of the present invention;

Figure 13 is a diagram view of a flexure arm and chuck used in the mechanical implementation of the switches disclosed in the present invention;

Figure 14 is a diagram view of a chuck assembly used in the mechanical implementation of the switches disclosed in the present invention; Figure 15 is a diagram view of an alternate embodiment of the flexure arm and chuck used in the mechanical implementation of the switches disclosed in the present invention;

Figure 16 is a diagram view of an alternate embodiment of a chuck assembly used in the mechanical implementation of the switches disclosed in the present invention;

Figure 17 is a detail view of a switch actuator used to actuate the flexure arms depicted in Figures 13-16;

Figure 18 is a detail view of a thrust bearing used in the flexure arms and chuck assemblies depicted in Figure 13-16;

Figure 1 is a graph comparing switching losses for a damped switch and a switch that has not been damped; and

Figure 20 is a diagram of an alternate chuck assembly used to implement the switches disclosed in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the Channel selector of the present invention is shown in Figure 1, and is designated generally throughout by reference numeral 10.

In accordance with the invention, the present invention for an optical switch or WADM 1 includes a channel selector 10. Channel selector 10 may include multiple single channel filter elements and a highly reflecting mirror that covers the wavelength range of interest. When implemented in an optical switch apparatus or a WADM, the channel selector 10 is movable in two orthogonal degrees of motion, making the switch or WADM channel selectable and reconfigurable without impacting adjacent channels. These features provide many advantages that are not found in conventional add/drop switch technologies. The present invention has low optical loss. The light signal is not filtered by tuning-through adjacent filters when changing wavelength channels. As a result, there is no cross-talk due to "tuning-through." The channel selector has low non-uniformity, is small in size, and integrated. The switches and WADMs that incorporate the channel selector are reconfigurable, and provide latching switch states. The basic design of the WADM or switch is a two-channel module. The two-channel modules can be cascaded to add/drop N-wavelengths, where N is an integer. As embodied herein and depicted in Figure 1, channel selector 10 according to a first embodiment of the present invention is disclosed. Channel selector 10 includes wavelength selector 100 and a reflector segment 110. Wavelength selector segmentlOO is an array of discrete wavelength channel filters 102-108, which each passing a spectral band corresponding to a wavelength channel. As shown, filter segment 102 transmits wavelength channel λi and reflects all other wavelength channels, in this case, wavelength channels λ₂ and λ₃.

As embodied herein and depicted in Fig. 2, wavelength channel selection in accordance with the present invention is disclosed. As shown, channel selector 10 is moved with respect to the optical beam to select a desired wavelength channel. In this example, channel selector 10 is reconfigured from passing wavelength channel λi to passing wavelength channel λ₂. One salient feature of the present invention is that reflector segment 110 is disposed adjacent to all channel filters 102-108. The arrangement of filter elements 102 -108 allows for channel selection capability without "tuning through" adjacent channels. Channel selector 10 is initially positioned such that wavelength channel λ] is selected by illuminating element 102. By moving filter switch 10 with respect to the incident beam to the high reflector, all of the wavelength channels are reflected. The selection of another channel is effected by moving channel selector 10 such that the relative movement of the beam is along reflector segment 110 until the beam is positioned adjacent to the selected filter 108. Channel selector 10 is then moved to position the optical beam onto the selected filter 108.

Since individual channel selectors access a different portion of the system spectrum, one of ordinary skill in the art will recognize that multiple channel selectors can be cascaded in a WADM or switch device. A set of four channel selectors 10, each having four different channel filters can be used to access any channel in a 16 wavelength channel system.

As embodied herein and depicted in Figure 3, a linearly variable channel selector 10 is disclosed in accordance with a second embodiment of the present invention. One of ordinary skill in the art will recognize that by moving linearly variable filter 100 as shown, channel selector 10 can be tuned to any center wavelength. When incorporated into an optical switch or WADM, a tunable optical switch or WADM is created. As embodied herein, and depicted in Figure 4, a channel selector 10 having two band pass filter segments, Al and A2, is disclosed in accordance with a third embodiment of the present invention. Wavelength selector segment 100 includes filter segment 114 that is tuned to wavelength channel Al and filter segment 116 that is tuned to wavelength channel A2. Wavelength channels Al and A2 are both tuned to the same wavelength channel. However, filter segment 114 (Al) has a narrow pass band, whereas filter segment 116 (A2) has a broad pass band. In this instance, channel Al has a 50 Ghz pass-band and channel A2 has a 100 GHz pass band. During the switching motion, the switch moves from reflector segment 110 to filter segment 114 to thereby provide a 50 GHz pass band. Systems using 50 Ghz wide channels typically separate adjacent channels by 0.4 nm. If channel A were to be configured as a 100 GHz wide channel, then the switch would move through Al to A2. Systems using 100 GHz channel widths typically separate adjacent channels by 0.8 nm. One of ordinary skill in the art will recognize that moving channel selector 10 through Al has no effect on any adjacent channels. As channel selector 10 settles into A2, there is no impact on adjacent -channels.

As embodied herein and depicted, in Figure 5, a channel selector 10 having two wavelength channel filters each including two pass-bands is disclosed in accordance with a fourth embodiment of the present invention. Wavelength selector segment 100 includes filter sub-segment 114 (Al), filter sub-segment 116 (A2), filter sub-segment 119 (Bl), and filter sub-segment 120 (B2). Filter sub-segment 114 passes wavelength channel A with a 50 GHz pass band. Filter sub-segment 116 passes wavelength channel A and has a 100 GHz pass band. Filter sub-segment 118 passes wavelength channel B and has a 50 GHz pass band. Filter sub-segment 120 passes wavelength channel B and has a 100 GHz pass band. Sub-segments 114,116, 118, and 120, are interleaved allowing channel selector 10 to shift from reflector segment 110 to sub- segments 114, 116, 118, or 120 directly. By interleaving the sub-segments, the light beam is directed onto the desired segment only, without the intermediate step associated with the channel selector 10 depicted in Figure 4. One of ordinary skill in the art will recognize that channel selector 10 can be implemented having a circular shape. Channel selector 10 can also be implemented to move in a circular motion as needed. As embodied herein and depicted in Figure 6, a method of manufacturing channel selector 10 is disclosed. First, substrate 130 is formed. Substrate 130 is masked using a photolithographic technique. Alternatively, it is cut into strips and masked mechanically before being coated with the subsequent layers that will be described below. Second, the broader spectral filter segment 116 is deposited on substrate 130. Subsequently, segment 116 is masked. The narrower filter segment 114 is then deposited over the unmasked portion of segment 116. Finally, broad band filter segment 116 and narrow band filter segment 114 are masked and a high reflective coating such as a gold film is applied to produce reflector segment 110. Reflector segment 110 may be of any suitable type, but there is shown by way of example a reflective metallic material. One of ordinary skill in the art will recognize that a dielectric material may also be used to fabricate reflector segment 110. The thickness of the gold film must be chosen appropriately to achieve high reflectance and minimize interference effects. It is noted that the switch will suffer small transient losses during switching from the effects of scattering at the gold film edge. However, the area of the edge is small compared to the area of the beam, and hence, the scattering losses are inconsequential. One of ordinary skill in the art will appreciate that each filter segment is matched in phase to adjacent filter segments.

As embodied herein and depicted in Figure 7, an alternate method of manufacturing channel selector 10 is disclosed. Layers of thin-films representing segmentsl 10, 114, and 116 are directly deposited onto substrate 130. A photolithographic masking process is used to ensure that segments 110, 114, and 116 are perfectly matched at the interfaces.

As embodied herein and depicted in Figure 8 A, a top view of a channel selector 100 according to a fifth embodiment of the present invention is disclosed. Channel selector 100 inlcudes a wavelength selector 102 and reflector 110. The materials used to fabricate channel selector 100 have been discussed previously with respect to the first four embodiments disclosed above. Wavelength selective filter 102 is fabricated to allow light of a specific wavelength to pass, and to reflect all other wavelengths. The pass band of filter 102 can be 50 GHz, lOOGhz, 200 GHz, or some other wavelength dependent function depending on the requirements of the system. Reflector 110 reflects all wavelengths of the incident light signal.

Figure 8B is a side view of the channel selector 100 shown in Figure 8 A. Wavelength selector 102 is deposited on substrate 130. Subsequently, reflector 110 is disposed on wavelength selective filter 102. There is a problem associated with this method of fabricating channel selector 100. The device tends to behave like a two- beam interferometer when the light beam is incident both filter 102 and reflector 110 during switching. The expression for the intensity of the incident light signal is given by the equation:

where β is the portion of the beam incident reflector 110, φ is the phase shift of the light reflected off of reflector 110, p(λ) is the reflection coefficient of the dielectric filter 102, θ(λ) is the phase shift of the light being reflected off of filter 102, and d is the thickness of the reflective layer. If designed improperly, an interference pattern can be established between the two beams, resulting in a loss of signal energy. This is avoided by adjusting thickness "d" of the reflector to cause the phase shift of filter 102 to be substantially equal to 2π times the phase shift of reflector 110. Thus, constructive interference mitigates losses during switching. Scattering can also be a problem in this design. Scattering losses are minimized by keeping the reflector edge as sharp as possible.

As embodied herein and depicted in Figure 9A, a top view of a segmented channel selector 100 according to a sixth embodiment of the present invention is disclosed. Channel selector 100 includes five wavelength selective filters 102, 104, 106, 108, and 112. Figure 9B is a side view of the channel selector shown in Figure

9A. Layers of thin-films representing segments 102, 104, 106, 108, and 112 are directly deposited onto substrate 130. As discussed above in relation to Figure 7, a photolithographic masking process is used to ensure that these segments are perfectly matched at the interfaces. Figure 9C is another side view of the channel selector shown in Figure 9 A. Again, when channel selector 100 is moved to switch the light signal from one of the segments to reflector 110, an interference pattern can be established between the two beams, if channel selector 100 is designed improperly. This is avoided by adjusting thickness "d" of the reflector to cause the phase shift of the filter segments to be substantially equal to 2% times the phase shift of reflector 110. As embodied herein and depicted in Figure 10, a two-channel drop switch 1 is disclosed. Switch 1 includes input port 20 which directs a light signal toward drop port 26. Channel selector 100 is disposed between input port 20 and drop port 26 and reflects the light signal toward drop port 22. Channel selector 200 is disposed between channel selector 100 and drop port 22 and ultimately, reflects the light signal toward output port 24.

Input port 20, drop ports 22 and 26, and output port 24 may be of any suitable type, but there is shown by way of example an optical fiber connected to a GRL lens or any other suitable collimator.

Channel selectors 100 and 200 may be of any suitable type, but there is shown by way of example in the detail view of Figure 8, channel selectors consisting of a single segment wavelength selector 102 (202) and a reflector segment 110 (210) in accordance with a fifth embodiment. Wavelength selector 102 passes wavelength channel λ] and reflects all other wavelength channels. Wavelength selector 202 passes wavelength channel λ₂ and reflects all other wavelength channels. Switch 1 operates as follows. Switch 1 independently moves channel selectors

100 and 200 in the direction A- A perpendicular to the optical beam to achieve switching. The relative motion of the beam with respect to the filter is shown in the detail view of Figure 8. For example, when channel selector 100 is positioned to have the beam incident filter segment 102, wavelength channel λi is resonant with the thin film filter segment 102, and wavelength channel λ] passes through channel selector 100 into drop port 26. The remaining channels are uniformly reflected from filter segment and directed toward channel selector 200. In similar fashion, if the incident beam is positioned on filter segment 202, wavelength channel λ passes through channel selector 200 into drop port 22. The remaining channels are directed by channel selectors 100 and 200 into output port 24. Switch 1 is reconfigured by moving either, or both channel selectors 100 and 200 to position the beam on reflecting segments 110 or 210, as desired. When the light signal is incident reflecting segments 110 or 210, all channels are uniformly reflected into output port 24. Thus, either λ] or λ₂, or both, can be dropped or included in the output signal directed into output port 24.

One of ordinary skill in the art will recognize that switch 1 as shown in Figure 10 can be converted into an add/drop switch by providing an add port for each drop port provided. As embnodied herein and depicted in Figure 11, a plan view of an Add/Drop switch 1 incorporating the channel selectors disclosed in the fourth and fifth embodiments of the present invention is disclosed. Add port 34 is disposed adjacent to drop port 26. When channel selector 100 is actuated such that the light signal is incident filter 102(not shown), wavelength channel 1 is directed into drop port 26. At the same time, add channel 1 is directed through filter 102 from the opposite direction and added to the light signal. In this embodiment add channel 1 is reflected only once from the opposing channel selector 200. Add port 32 is disposed adjacent to drop port 22. When channel selector 200 is actuated such that the light signal is incident filter 202(not shown), wavelength channel 2 is directed into drop port 22. At the same time, add channel 2 is directed through filter 202 from the opposite direction and added to the light signal being directed into output port 24.

One of ordinary skill in the art will recognize that switch 1 as shown in Figure 10 and Figure 11 can be cascaded to accommodate more wavelength channels.

As embodied herein and depicted in Figure 12, a WADM 1 using the channel selectors shown in Figures 10 or 11 is disclosed. Input port 20 directs the light signal into WADM 1, toward channel selector 100, which selectively filters wavelength channel λi. As discussed above, when reflector segment 110 (Figure 10 or 11) is in the path of the light beam, all wavelength channels are reflected toward channel selector 200 (λ₂). If the light signal is incident filter segment 102, wavelength channel λ} is directed into drop port 26. At the same time, add port 34 directs add channel λ_\ into

WADM 1 through the opposite side of filter segment 102 and add channel λi is inserted into the outgoing optical beam toward channel selector 200 (λ₂ ). One of ordinary skill in the art will recognize that add ports 32, 34, 36, and 38 can be disposed next to their respective drop ports as shown in Figure 11. As depicted, channel selector 200 is optically coupled to channel selector 300(λ₃ ). Depending on the position of channel selector 300, wavelength channel λ₃ can be dropped into drop port 28 and a corresponding add channel can be added via add port 38. Channel selector 300 is optically coupled to channel selector 400 (λ_N ). Again, depending on the position of channel selector 400, wavelength channel λ^ can be dropped into drop port 30 and a corresponding add channel can be added via add port 36. Finally, the output light signal reflects off channel selector 400 into output port 24. Channel selectors 100-400 are actuated independently. Thus, an N-stage cascaded device can independently drop or add N-wavelength channels. One of ordinary skill in the art will recognize that other channel selector configurations (see Figures 2-8) can be used depending on system needs.

As embodied herein and depicted in Figure 13, a perspective view of switch 1, showing mechanical actuation details is disclosed. Flexure arms 50 and 60 are used to actuate channel selectors 100-400 in the switch and WADM depicted in Figures 8 and 9, respectively. Channel selector 100 is mounted in chuck 52 on flexure arm 50. Channel selector 200 is mounted in chuck 62 on flexure arm 60. Flexure structures 54 and 64 provide fine angular adjustments as well as coarse angular adjustments with two degrees of freedom. Flexure structure 54 in flexure arm 50 provides an angle adjustment in the horizontal plane and flexure structure 64 in flexure arm 60 provides angular adjustments in the vertical plane. Angular adjustments are achieved by inserting a proper tool into slot to bend the flexures in either direction. The size of the deforming flexure member in each flexure 54 and 64 is chosen to provide adequate mechanical strength in combination with adequate deformability by the special tooling.

These angular adjustments provided by flexures 54 and 64 allow channel selectors 100 and 200 to be aligned to each other within 20 arc seconds (100 micro-radians). Flexure arms 50 and 60 also include indented regions 588 and 688, respectively. These regions are provided to accomodate thrust bearings 58 and 68, respectively. Flexure arms 50 and 60 also include holes 586 and 686, respectively. Holes 586 and 588 are used to accommodate a connector or screw (not shown) which acts as a pivot or axle. The screw is co-linear with the axis of rotation. This arrangement will be discussed in more detail below.

As embodied herein and depicted in Figure 14, a perspective view of chuck assembly 70 is disclosed in accordance with the present invention. The switch 1 disclosed in Figure 8 is housed by base plate 72. The various compartments formed in base plate 72 were formed by a machining process to accommodate collimators 20, 22, 24, and 26, solenoids 56 and 66, and flexure arm assemblies 50 and 60 depicted in Figure 13. One of ordinary skill in the art will recognize that it is a relatively simple task to produce more compartments in a larger block of aluminum when implementing the WADM depicted in Figure 12. In one embodiment of the chuck assembly depicted in Figure 14, flexure arms

50 and 60 are movable with one degree of freedom. Thrust bearing assemblies 58 and 68 are formed around flexure arms 50 and 60 and are attached to base plate support 74. Thrust bearings 58 and 68 are fastened with a spring-loaded connector on base plate support 74 to form a pivot co-linear with the axis of rotation. Thrust bearings 58 and 68 limit the movement of flexure arms 50 and 60 in directions orthogonal to the direction of rotational motion. Channel Selectors 100 and 200 are mounted to chucks 52 and 62, which are indented regions formed at the ends of flexure arms 50 and 60, respectively. Flexure arms 50 and 60 are rotatable around the axis of rotation and move channel selectors 100 and 200 between two or more positions in switch 1, depending on the type of channel selectors used (See Figures 2-8). Actuators 56 and 66 are coupled to flexure arms 50 and 60, respectively. Actuators 56 and 66 actuate the flexure arms causing them to rotate about the rotational axis within a range of 4 degrees to obtain the channel selector functions discussed above for adding or dropping a wavelength channel. In another embodiment, two-degrees of freedom can be incorporated into switch 1 by mounting two mini slides (not shown) under thrust bearing assemblies 58 and 68. In this embodiment, base plate 70 is machined to accommodate two additional solenoids for actuating the two mini-slides.

Actuators 56 and 66 may be of any suitable type, but there is shown by way of example magnetic latching bi-state solenoids. One of ordinary skill in the art will recognize that a commercially available latching relay is also be suitable.

As embodied herein and depicted in Figure 15, a diagram view of an alternate embodiment of the flexure arm and chuck used in the mechanical implementation of the switches disclosed in the present invention is disclosed. The reference numbers used in this embodiment are identical to those used in Figure 13 with some additional features. As discussed above, flexure arms 50 and 60 are used to actuate channel selectors 100 and 200. Channel selector 100 is mounted in chuck 52 on flexure arm 50. Channel selector 200 is mounted in chuck 62 on flexure arm 60. Both flexure structure 54 and 64 provide fine ^"angular adjustments as well as coarse angular adjustments with two degrees of freedom. Referring to the coordinate system shown in Figure 15, flexure structures 54 and 64 are adjusted to position the light incident faces of channel selectors 100 and 200 to be parallel to the plane of rotation within 20 arc seconds (100 micro- radians). This guarantees a variation of insertion loss during switching to be below 0.3 dB. The plane of rotation is defined by the swinging motion of the flexure arms around the axis of rotation. Each flexure can be bent in both the horizontal plane (x-y), vertical plane (y-z), or twisted about the y-axis. In making these adjustments, a tool is inserted into holes next to flexures 54 or 64 to bend them in the desired direction. Subsequently, locking pad 589 is disposed and fixed into recessed region 587 and locking pad 689 is disposed and fixed into recessed region 687. Locking pads 589 and 689 are made of the same material as flexures 54 and 64, respectively. In one embodiment, the locking pads 589 and 689 are glued to the recessed regions 587 and 687, respectively. One of ordinary skill in the art will recognize that other methods of attaching the locking pads can be used, depending for example, on whether the locking pads are removable. The size of the deforming flexure beam in each flexure 54 and 64 is chosen to provide adequate deformability when adjusted using the special tooling. In addition, the deforming flexure beams must have adequate mechanical strength in combination with the attached locking pads. Flexure arms 50 and 60 also include indented regions 588 and 688, respectively. These regions are provided to accommodate miniature thrust bearings 58 and 68, respectively. Counterweights 585 and 685 are designed to balance channel selectors 100 and 200 with respect to rotation axis as defined by thrust bearings 58 and 68. Counterweights 585 and 685 make switch 1 insensitive to external vibrations. Flexure arms 50 and 60 also include holes 586 and 686, respectively. Holes 586 and 686 are used to fasten a bracket to actuate rotation of the flexure arms.

As embodied herein and depicted in figure 16, a diagram view of an alternate embodiment of a chuck assembly 10 used in the mechanical implementation of the switches disclosed in the present invention is disclosed. Chuck assembly 10 includes optical plate 70. The various compartments formed in optical plate 70 are formed by a mechanical machining process. These compartments accommodate collimators 20, 22, 24 and 26, solenoids 56 and 66, and flexure arm assemblies 50 and 60. In one embodiment of chuck assembly 10, flexure arms 50 and 60 are movable with one degree of freedom. As discussed above, mini-slides are provided when two degrees of freedom are needed for the segmented channel selectors. Flexure arms 50 and 60 are connected to axial support mount 74 to form a pivot around the axis of rotation. Thrust bearing assemblies 58 and 68 are formed around flexure arms 50 and 60. Axial support mount 74 includes two flexure structures 740 and 742, respectively. Flexures 740 and 742 provide angular adjustment for two flexure arms 50 and 60 in both horizontal and vertical planes so that their respective planes of rotation can be adjusted to be parallel to each other. Flexure 740 provides angular adjustment for flexure arm 50 in horizontal plane x-y and flexure 742 provides angular adjustment for flexure arm 60 in vertical plane y-z. Flexures 740 and 742 are bent to achieve the required parallelism by inserting a tool in a tapped hole machined in flexures 740 and 742, respectively. After the adjustments, locking pad 724 is attached to a recessed region in the top of flexures 740 and 742 to provide sufficient mechanical strength for reliable operation. As embodied herein and depicted in Figure 17, a detail view of the actuation mechanism of flexure arms 50 and 60 is disclosed. The description relates to flexure arm 50, but one of ordinary skill in the art will recognize that the description is equally applicable to flexure arm 60 as well. Flexure arm 50 includes holes 566 and 568 which accommodate damping springs 562 and 564. Plunger 560 of solenoid 56 pushes damping leaf spring 560 toward flexure arm 50. Arm 562 of damping leaf spring 560 is disposed in hole 566 and acts to push flexure arm 50 downward. This downward movement causes flexure arm 50 to rotate around the axis of rotation, to thereby move channel selector 200 (Figures 13-16) into position. Damping spring 564 is connected to base plate support 74 and is inserted into hole 568. Spring 564 resists the downward movement of flexure arm 50 and supplies a damping resistance that mitigates unwanted vibrations that would otherwise result in jitter.

As embodied herein and depicted in Figure 18, a detail view of thrust bearing assembly 58 is disclosed. One of ordinary skill in the art will recognize that the description is equally applicable to thrust bearing assembly 68. As discussed above, flexure arm 50 includes indented regions 588 which are disposed about hole 586.

Thrust bearings 584 fit within indented regions 588. Screw 580 is disposed in holes 586 and 686. As discussed above, flexure arm 50 and thrust bearings 584 rotate around screw 580 allowing 4° of movement between switch positions. Screw 580 presses against wave washer 582 and thrust bearings 584 to form spring loaded thrust bearing assembly 58. Screw 580 applies approximately 4 lb. of force to thrust bearings 584. This force substantially eliminates channel selector jittering during rotational movement. Thrust bearing assembly 58 exceeds the vibration/shock requirement set by

Bellcore standards. The thrust bearings 584 used in assembly 58 are designed for rotation of 500 rpm (revolution per min) with a long lifetime. Thus, the design is durable and reliable. Any wearing that does occur will be compensated for by the spring-loading mechanism 582. Figure 19 is a plot showing the improvement in transient excess loss due to the use of thrust bearing assemblies 58 and 68 discussed above. The plot represents the excess loss that is generated in neighboring wavelength channels when flexure arm 50 is actuated to move channel selector 100 to drop wavelength channel λl. Curve 300 shows actuation of wavelength channel λl. As shown by curve 304, wavelength channel λ3 experiences significant vibrations without the damping provided by thrust bearing assembly 58. This results in transient excess-loss greater than 15dB for a maximum duration of 100msec. As shown by curve 306, wavelength channel λ3 experiences less than 0.5 dB excess loss with the damping provided by thrust bearing assembly 58. Note that with the damping, the excess loss occurs within the 10msec switch actuation time.

As embodied herein and depicted in Figure 20, a diagram of an alternate chuck assembly 80 is disclosed. Channel selector 100 is disposed and glued into chuck 52. Chuck 52 is an indented region formed at one end of flexure arm 50. Channel selector 200 is disposed and glued into chuck 62. Chuck 62 is an indented region formed at one end of flexure arm 60. Flexure arms 50 and 60 are connected to Schneeberger micro- frictionless slides 70 and 90, respectively. Slides 70 and 90 provide a very smooth motion with a deviation from the plane of motion of under 2 microns. Slide 70 is indirectly connected to solenoid 56 via spring 74 and arm 50. Slide 90 is indirectly connected to solenoid 66 via spring 94 and arm 60. Flexure arm 50 is connected to a second spring 72, whereas flexure arm 60 is connected to spring 92. Springs 72 and 92 act as a loading force on linear slides 70 by being bolted onto flexure arms 50 and 60, respectively. This arrangement ensures a smoother motion. Flexure arm 50 is mounted onto flexure member 54, which has a motion horizontal to the beam path. Flexure arm 60 is mounted on flexure member 64, which has a motion perpendicular to the beam path. This arrangement is very similar to the first mechanical implementation discussed above. Flexure members 54 and 64 provide a means for ensuring beam parallellism, and tuning the incident angle of the light beam onto channel selectors 100 and 200.

Solenoids 56 and 66 are magnetic latching, bi-state solenoids. For example, magnets 560 are provided at either end of solenoid 56. Solenoid 66 is also equipped with magnets 660. Solenoids 56 and 66 are encapsulated in a vibration absorbing foam which further serves to mitigate the effects of vibration on transient excess loss. Springs 74 and 94 serve to absorb vibrations inherent in the switching motion of solenoids 56 and 66. Springs 72 and 92 oppose the motion of solenoids 56 and 66, respectively. Vibrations are reduced by slowing down the motion of the solenoid at the end of the stroke. Thus, vibrations are further damped, and a smooth return force is ensured when the solenoids retract. Thus, the plot depicted in Figure 19 is applicable to the chuck assembly of Figure 20, as well.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. An optical device for directing a light signal having a plurality of wavelength channels, said optical device comprising: a wavelength selecting filter that transmits a selected wavelength channel and reflects non-selected wavelength channels, wherein said wavelength selecting filter causes said reflected non-selected wavelength channels to have a first phase shift; and a reflector disposed on a portion of said wavelength selecting filter, said reflector having a reflector thickness that is selected to cause a reflected light signal to have a second phase shift that is substantially equal to an integer multiple of 2π times said first phase shift.

2. The optical device of claim 1, wherein the wavelength selecting filter comprises an array of discrete filter elements.

3. The optical device of claim 2, wherein a wavelength channel is selected by moving the wavelength selecting filter such that the light signal is incident a corresponding discrete filter segment tuned to said wavelength channel.

4. The optical device of claim 1, wherein an intensity of a reflected light signal during switching is characterized by:

wherein β is a portion of the light signal incident the reflector, φ is the second phase shift, p(λ) is a reflection coefficient of the wavelength selecting filter, θ(λ) is the first phase shift, and d is the reflector thickness.

5. The optical device of claim 1, wherein the wavelength selecting filter has a pass band that is approximately equal to 50 GHz.

6. The optical device of claim 1, wherein the wavelength selecting filter has a pass band that is approximately equal to 100 GHz.

7. The optical device of claim 1, wherein the wavelength selecting filter has a pass band that is approximately equal to 200 GHz.

8. The optical device of claim 1, wherein the wavelength selecting filter segment and the reflector segment are disposed on a substrate to form a channel selector.

9. The optical device of claim 8 further comprising: an input port coupled to the channel selector, said input port directing the light signal into the optical device; a chuck assembly for holding the channel selector and moving the channel selector between a first position and a second position relative to the light signal; a drop port coupled to the channel selector, wherein the selected wavelength channel is directed into said drop port when the channel selector is in said first position; and an output port coupled to the channel selector, wherein the non-selected wavelength channels are directed into said output port when the channel selector is in said first position and the reflected light signal is directed into said output port when the channel selector is said second position.

10. The optical device of claim 9, wherein the chuck assembly further comprises: an optical plate for securing the input port, the output port, the add port and the drop port in fixed positions relative to each other, said optical plate including an adjustable axial support member that defines an axis of rotation; and a flexure arm having a chuck disposed on a first end for holding the channel selector in a fixed position relative to said flexure arm, and connected at a second end to said adjustable axial support member at said axis of rotation to form a pivot, whereby said flexure arm is rotatable around said pivot in a plane of rotation.

11. The optical device of claim 10, further comprising an add port coupled to the channel selector, wherein said add port directs an add channel occupying a spectral region substantially the same as the selected wavelength channel is directed into the optical device when the channel selector is in the first position.

12. The optical device of claim 11, wherein the flexure arm comprises a flexure stracture whereby the first end is adjusted relative to the second end to thereby align the channel selector to the plane of rotation.

13. The optical device of claim 12, wherein the flexure structure is adjustable in at least two dimensions.

14. The optical device of claim 12, wherein the flexure structure is adjusted to cause a light incident face of the channel selector to be parallel to the plane of rotation.

15. The optical device of claim 12, further comprising a locking pad mounted on a flexure member, whereby said locking pad prevents movement by the flexure member after the channel selector is aligned to the plane of rotation.

16. The optical device of claim 11, further comprising a counterweight connected to said second end, to thereby balance the channel selector with respect to the axis of rotation.

17. An optical device for directing a light signal having a plurality of wavelength channels, said optical device including an input port, a plurality of drop ports, and an output port, said optical device comprising: a plurality of channel selectors coupled to the input port, the plurality of drop ports, and the output port, wherein each channel selector selectively transmits a wavelength channel into a corresponding drop port; a plurality of flexure arms, each of said flexure arms having a chuck disposed at a first end for holding a corresponding channel selector, and a pivoting member at a second end, whereby said flexure arm is rotatable around an axis of rotation to move said channel selector in a plane of rotation between a first position and a second position; and an optical plate having an axial support member connected to each of said pivoting members at said axis of rotation, whereby said axial support member is adjustable to align said plurality of flexure arms such that their planes of rotation are substantially parallel.

18. The optical device of claim 17, wherein each channel selector further comprises: wavelength selecting filter that transmits a selected wavelength channel and reflects non-selected wavelength channels in the first position, wherein said wavelength selecting filter causes said reflected non-selected wavelength channels to have a first phase shift; and a reflector disposed on a portion of said wavelength selecting filter, said reflector having a reflector thickness that is selected to cause a reflected light signal to have a second phase shift that is substantially equal to an integer multiple of 2π times said first phase shift, whereby the light signal is incident said reflector in the second position.

19. The optical device of claim 18, wherein a selected wavelength channel is directed into a predetermined drop port when the channel selector is in the first position.

20. The optical device of claim 18, wherein non-selected wavelength channels are directed into the output port.

21. The optical device of claim 18, further comprising a plurality of add ports, each of said add ports is coupled to a corresponding channel selector, whereby an add channel is directed into the optical device when the selected wavelength channel is directed into the drop port.

22. The optical device of claim 21, wherein the add channel is added to the light signal by being transmitted through the wavelength selecting filter and once reflected off of an opposing channel selector.

23. The optical device of claim 21, wherein the selected wavelength channel and the add channel occupy a spectral region that has substantially the same set of wavelengths.

24. A method of fabricating an optical device, said method comprising the steps of: providing a wavelength selective filter that transmits light having a predetermined spectral pass band and reflects light outside said predetermined spectral pass band, whereby said wavelength selective filter causes filter-reflected light to have a first phase shift; and disposing a reflector on a portion of said wavelength selecting filter, said reflector having a reflector thickness that is selected to cause reflector- reflected light to have a second phase shift that is substantially equal to an integer multiple of 2π times said first phase shift.

25. A method of fabricating an optical device for directing a light signal having a plurality of wavelength channels, said method comprising the steps of: providing a chuck assembly that includes a plurality of flexure arms each having a chuck disposed at a first end, a flexure member, and a pivoting member disposed at a second end, and an optical plate having an axial support member, whereby each of said pivoting members is connected to said axial support member and rotatable around an axis of rotation in a plane of rotation; attaching a channel selector to each chuck, each of said channel selectors including a reflector disposed on a wavelength selective filter, whereby said wavelength selective filter transmits one wavelength channel and said reflector reflects all of the wavelength channels; adjusting each of said flexure members to cause a light incident side of each channel selector to be parallel to its respective plane of rotation; and adjusting the axial support member to thereby align said plurality of flexure arms such that their planes of rotation are substantially parallel.

26. The method of claim 25, wherein the wavelength selective filter transmits a predetermined wavelength channel and reflects all other wavelength channels, whereby said wavelength selective filter causes filter-reflected light to have a first phase shift, and the reflector has a reflector thickness that is selected to cause reflector-reflected light to have a second phase shift that is substantially equal to an integer multiple of 2π times said first phase shift.

27. The method of claim 25, further comprising the steps of: connecting an input port to the optical plate and coupling said input port to the channel selector, whereby said input port directs the light signal into the optical device; connecting a drop port to the optical plate and coupling said drop port to the channel selector, wherein the predetermined wavelength channel is directed into said drop port when the channel selector is in a first position; and connecting an output port to the optical plate and coupling said output port to the channel selector, wherein filter-reflected light is directed into said output port when the channel selector is in said first position and said reflector-reflected light is directed into said output port when the channel selector is in a second position.

28. The method of claim 27, further comprising the step of providing a plurality of add ports, each of said add ports is coupled to a corresponding channel selector, whereby an add channel is directed into the optical device when the predetermined wavelength channel is directed into the drop port.