WO2019173059A1

WO2019173059A1 - Optical add-and-drop multiplexer devices

Info

Publication number: WO2019173059A1
Application number: PCT/US2019/018900
Authority: WO
Inventors: Dong GUI; Chen Xia; Andy Fenglei Zhou
Original assignee: Alliance Fiber Optic Products, Inc.
Priority date: 2018-03-07
Filing date: 2019-02-21
Publication date: 2019-09-12

Abstract

Disclosed herein are optical add-and-drop multiplexer devices. In particular, disclosed is an optical add-and-drop multiplexer (OADM) device including two common ports and two reflection ports within two dual fiber pigtails associated with a single housing. The two common ports transmit a transmission signal of a multiplexed signal along an optical path therebetween. At least one wave-division multiplexing (WDM) filter having a passband is positioned in the optical path between the first common port and the second common port to route add and drop demultiplexed signals to the reflection ports. A portion of the optical path extending between a first side and a second side of the at least one WDM filter is devoid of an optical fiber. Accordingly, the four-port OADM device provides a number of improvements and advantages, such as a simpler, more economic, more compact design with better optical performance.

Description

OPTICAL ADD-AND-DROP MULTIPLEXER DEVICES

PRIORITY APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 62/639,663, filed on March 7, 2018, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

[0002] The disclosure relates to wavelength-division multiplexing and demultiplexing, and more particular, to an optical add-and-drop multiplexer (OADM) with add and drop paths.

[0003] Wavelength-division multiplexing (WDM) is a technology that multiplexes (e.g., adds) a number of distinct wavelengths of light onto a single optical fiber and demultiplexes (e.g., divides) a number of distinct wavelengths of light from a single optical fiber, thereby increasing information capacity and enabling bi-directional flow of signals. Multiple optical signals are multiplexed with different wavelengths of light combined by a multiplexer at a transmitter, directed to a single fiber for transmission of the signal, and split by a demultiplexer to designated channels at a receiver. By combining multiple channels of light into a single channel, WDM assemblies and associated devices can be used as components in an optical network, such as a passive optical network (PON).

[0004] FIG. 1 is a diagram illustrating optical paths for an optical add-and-drop multiplexer (OADM) 100. An OADM device 100 is a device designed for routing specific optical wavelengths into (i.e., add) or out of (i.e., drop) optical paths ln certain configurations, the OADM device 100 includes a first communication port 102 and a second communication port 104. ln between the first communication port 102 and the second communication port 104 is a main optical path 106. A plurality of drop ports 108A-108D (e.g., li -A) are in optical communication with the main optical path 106 by a plurality of drop paths 110A-110D, and a plurality of add ports 112A-112D (e.g., l_h+i-l_h+4) are in optical communication with the main optical path 106 by a plurality of add paths 114A-114D. OADM devices 100 are increasingly relied upon in the construction of fiber communication infrastructure, especially in the deployment of WDM to optical networks. OADM devices 100 are used as optical nodes in optical transport networks (OTNs) since the OADM device 100 provides signal add/drop in an optical line without optical-electrical-optical conversion. [0005] FIG. 2 is a cross-sectional top view of a three-port thin-film-filtcr (TFF) device 200. The three-port TFF device 200 includes a first collimator 202 and a second collimator 204 in optical communication with the first collimator 202. The first collimator 202 includes a first common port 206 (to transmit multiplexed signals) and a reflection port 208 (or R-port) (to add or drop a signal), and the second collimator 204 includes a second common port 210 (to transmit multiplexed signals) ln particular, the first collimator 202 includes a dual fiber pigtail 212, a G-lens 214 (may also be referred to as a gradient-index (GR1N) lens), and a thin- film-filter 216, and the second collimator 204 includes a single fiber pigtail 218 and a C-lens 220 (may also be referred to as a collimating lens). As a multiplexed signal is transmitted between the common ports 206, 210, the multiplexed signal must travel through five optical interfaces or optical couplings, including a first interface between the dual fiber pigtail 212 and the G-lens 214, a second interface between the G-lens 214 and the thin- film-filter 216, a third interface between the thin-film-filter 216 and free space 217, a fourth interface between the free space 217 and the C-lens 220, and a fifth interface between the C-lens 220 and the single fiber pigtail 218. The three-port TFF device 200 is able to add or drop a signal from the main optical path, but cannot do both (i.e., cannot both add and drop signals). To add and drop a signal from the main optical path, two three-port TFF devices 200 must be placed in series.

[0006] FIG. 3 is a cross-sectional top view of a three-port TFF assembly 300 of two three- port TFF devices 200-1, 200-2 connected in series to provide a drop path 302 and an add path 304. The second common port 210-1 of the first three-port TFF device 200-1 is optically connected to the second common port 210-2 of the second three-port TFF device 200-2. For a multiplexed signal to transmit from the first common port 206-1 of the first three-port TFF device 200-1 to the first common port 210-2 of the second three-port TFF device 200-2, the multiplexed signal must travel through ten optical interfaces (i.e., five interfaces in each of the three-port TFF devices 200). There may be a signal loss associated with each optical interface or optical coupling, which may increase in the aggregate (i.e., as more three-port TFF devices 200 are placed in series). Further, such a configuration can be bulky, difficult and expensive to manufacture, and require a large footprint, particularly in the aggregate (i.e., as more three- port TFF devices 200 are placed in series).

[0007] No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents. SUMMARY

[0008] Disclosed herein are optical add-and-drop multiplexer devices ln particular, disclosed is an optical add-and-drop multiplexer (OADM) device including two common ports and two reflection ports associated with (e.g., within) a single housing. The OADM device includes a first dual fiber pigtail including a first common port and a first reflection port, and a second dual fiber pigtail including a second common port and a second reflection port. The two common ports are configured to transmit a transmission signal of a multiplexed signal along an optical path therebetween. At least one wave-division multiplexing (WDM) filter has a passband positioned in an optical path between the first common port and the second common port. The at least one WDM filter has a first side and a second side opposite the first side, where a portion of the optical path that extends between the first side and the second side of the at least one WDM filter is devoid of an optical fiber. The at least one WDM filter routes drop demultiplexed signals from the first common port to the first reflection port, and routes add demultiplexed signals from the second reflection port to the second common port. Accordingly, the OADM device provides a number of improvements and advantages, particularly over the three-port TFF device discussed above ln particular, the OADM device may provide a simpler, more economic, more compact design using fewer components. The OADM device may also achieve better optical performance by reducing the number of interfaces required to add and drop demultiplexed signals between the two common ports.

[0009] One embodiment of the disclosure relates to an optical add-and-drop multiplexer (OADM) device. The OADM device includes a first common port, a second common port, a first reflection port, a second reflection port, and at least one wave-division multiplexing (WDM) filter. The first common port is configured for optical communication of a first multiplexed signal comprising a transmission signal and a first demultiplexed signal. The second common port is configured for optical communication of a second multiplexed signal comprising the transmission signal and a second demultiplexed signal. The first reflection port is configured for optical communication of the first demultiplexed signal. The second reflection port is configured for optical communication of the second demultiplexed signal. The at least one WDM filter has a passband. The at least one WDM filter is positioned in an optical path between the first common port and the second common port. The at least one WDM filter has a first side and a second side opposite the first side. A portion of the optical path extends between the first side and the second side of the at least one WDM filter is devoid of an optical fiber. The at least one WDM filter is configured to route (i) the first demultiplexed signal of the first multiplexed signal from the first common port to the first reflection port, (ii) the transmission signal from the first common port to the second common port, and (iii) the second demultiplexed signal from the second reflection port to the second common port to at least partially form the second multiplexed signal.

[0010] An additional embodiment of the disclosure relates to an optical add-and-drop multiplexer (OADM) device. The OADM device includes a first dual fiber pigtail positioned within a housing, a second dual fiber pigtail at least partially positioned within the housing, and at least one wave-division multiplexing (WDM) filter. The first dual fiber pigtail includes a first common fiber and a first reflection fiber. The first common fiber is configured for optical communication of a first multiplexed signal including a transmission signal and a first demultiplexed signal. The first reflection fiber is configured for optical communication of a first demultiplexed signal. The second dual fiber pigtail includes a second common fiber and a second reflection fiber. The second common fiber is configured for optical communication of a second multiplexed signal comprising the transmission signal and a second demultiplexed signal. The second reflection fiber is configured for optical communication of the second demultiplexed signal. The WDM filter has a passband. The at least one WDM filter is positioned in an optical path between the first common fiber and the second common fiber. The at least one WDM filter has a first side and a second side opposite the first side. A portion of the optical path extends between the first side and the second side of the at least one WDM filter is devoid of an optical fiber. The at least one WDM filter is configured to route (i) the first demultiplexed signal of the first multiplexed signal from the first common fiber to the first reflection fiber, (ii) the transmission signal from the first common fiber to the second common fiber, and (iii) the second demultiplexed signal from the second reflection fiber to the second common fiber to at least partially form the second multiplexed signal.

[0011] An additional embodiment of the disclosure relates to a method of using an optical add-and-drop multiplexer (OADM) device. The method includes transmitting from a first common port a first multiplexed signal comprising a transmission signal and a first demultiplexed signal. The method further includes routing using a first WDM filter the first demultiplexed signal of the first multiplexed signal from the first common port of a first dual fiber pigtail to a first reflection port of the first dual fiber pigtail and transmitting the transmission signal toward a second common port. The method further includes routing using a second WDM filter a second demultiplexed signal from a second reflection port of a second dual fiber pigtail to the second commonport of the second dual fiber pigtail such that the second demultiplexed signal and the transmission signal form a second multiplexed signal and transmitting the second multiplexed signal to the second common port.

[0012] Additional features and advantages 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 embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0013] lt is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a diagram illustrating optical paths for an optical add-and-drop multiplexer (OADM);

[0015] FIG. 2 is a cross-sectional top view of a three-port thin- film-filter (TFF) device;

[0016] FIG. 3 is a cross-sectional top view of an assembly of two three-port TFF devices of FIG. 2 connected in series to provide a drop path and an add path;

[0017] FIG. 4A is a cross-sectional top view of a OADM device including a first collimator and a second collimator;

[0018] FIG. 4B is close up cross-sectional top view of the first and second collimators of the OADM device of FIG. 4A illustrating dropping and adding signals using two WDM filters;

[0019] FIG. 5 is a cross-sectional top view of an OADM assembly with two OADM devices of FIGS. 4A-4B connected in series;

[0020] FIG. 6 is a top view of another embodiment of the OADM device of FIGS. 4A-4B with two WDM filters attached respectively to two dual fiber pigtails and separated by free space;

[0021] FIG. 7 is a top view of another embodiment of the OADM device of FIG. 6 with two WDM filters attached respectively to two dual fiber pigtails and separated by an intermediate layer; [0022] FIG. 8 is a top view of another embodiment of the OADM devices of FIGS. 4A- 4B with two WDM filters attached respectively to two dual fiber pigtails and abutting each other;

[0023] FIG. 9 is a top view of another embodiment of the OADM devices of FIGS. 4A- 4B with a single WDM filter attached to two dual fiber pigtails;

[0024] FIG. 10A is a side view of a WDM filter including a dielectric layer deposited on a glass substrate for use with the OADM devices of FIGS. 4A-9;

[0025] FIG. 10B is a side view of a WDM filter including two dielectric layers deposited on opposing sides of a glass substrate for use with the OADM devices of FIGS. 4A-9;

[0026] FIG. 10C is a side view of a WDM filter including one dielectric layer without a glass substrate for use with the OADM devices of FIGS. 4A-9;

[0027] FIG. 11 is a top view of a non-linear arrangement of the first and second dual fiber pigtails of the OADM device of FIGS. 6;

[0028] FIG. 12A is a flowchart of steps for manufacturing an OADM optical device of

FIGS. 4A-9;

[0029] FIG. 12B is a flowchart of steps for using an OADM optical device of FIGS. 4A-

9;

[0030] FIG. 13 is a perspective view of an example steel-tube collimator for use with the OADM devices of FIGS. 4A-11;

[0031] FIG. 14A is a perspective view of an example square tube collimator for use with the OADM devices of FIGS. 4A-11 ;

[0032] FIG. 14B is a cross-sectional top view of the square tube collimator of FIG. 14A;

[0033] FIG. 15A is a side view of an example compact collimator for use with the OADM devices of FIGS. 4A-11; and

[0034] FIG. 15B is a close-up side view of the compact collimator of FIG. 15A.

DETAILED DESCRIPTION

[0035] Reference will now be made in detail to the present preferred embodiments, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0036] Terms such as “left,” “right,” “top,” “bottom,” “front,” “back,” “horizontal,” “parallel,”“perpendicular,”“vertical,”“lateral,”“coplanar,” and similar terms are used for convenience of describing the attached figures and are not intended to limit this description. For example, terms such as“left side” and“right side” are used with specific reference to the drawings as illustrated and the embodiments may be in other orientations in use. Further, as used herein, terms such as“horizontal,”“parallel,”“perpendicular,”“vertical,” “lateral,” etc., include slight variations that may be present in working examples.

[0037] As used herein, the terms“optical communication,”“in optical communication,” and the like mean, with respect to a group of elements, that the elements are arranged such that optical signals are passively or actively transmittable therebetween via a medium, such as, but not limited to, an optical fiber, one or more ports, free space, index-matching material (e.g., structure or gel), reflective surface, or other light directing or transmitting means.

[0038] As used herein, the term“port” means an interface for actively or passively passing (e.g., receiving, transmitting, or both receiving and transmitting) optical signals. A port may include, by way of non-limiting examples, one or more fiber optic connectors, optical splices, optical fibers, free-space, or a combination of the foregoing.

[0039] As used herein, the term“pigtail” means a one or more optical fibers that extend from a ferrule. The one or more optical fibers may each be terminated with a fiber optical connector but are not required to be terminated a fiber optic connector.

[0040] Disclosed herein are optical add-and-drop multiplexer devices ln particular, disclosed is an optical add-and-drop multiplexer (OADM) device including two common ports and two reflection ports associated with a single housing. The OADM device includes a first dual fiber pigtail including a first common port and a first reflection port, and a second dual fiber pigtail including a second common port and a second reflection port The two common ports are configured to transmit a transmission signal of a multiplexed signal along an optical path therebetween. At least one wave-division multiplexing (WDM) filter has a passband positioned in an optical path between the first common port and the second common port. The at least one WDM filter has a first side and a second side opposite the first side, where a portion of the optical path that extends between the first side and the second side of the at least one WDM filter is devoid of an optical fiber. The at least one WDM filter routes drop demultiplexed signals from the first common port to the first reflection port, and routes add demultiplexed signals from the second reflection port to the second common port. Accordingly, the OADM device provides a number of improvements and advantages, particularly over the three-port TFF device ln particular, the OADM device may provide a simpler, more economic, more compact design using fewer components. Further, the OADM device may achieve better optical performance by reducing the number of interfaces required to add and drop demultiplexed signals between the two common ports. [0041] FIG. 4A is a cross-sectional top view of a OADM device 400 (may also be referred to as an OADM assembly) including a first collimator 402A generally aligned with a second collimator 402B along a central axis A-A of the housing 404. lt is noted that the first collimator 402A is slightly offset from the second collimator 402B. ln other words, a central axis of the first collimator 402A is slightly offset from a central axis of the second collimator 402B. The first collimator 402A and the second collimator 402B are at least partially positioned within a single housing 404 (may also be referred to as an OADM housing). The first collimator 402A includes or is in optical communication with a first common port 406A and a first reflection port 408A, and the second collimator 402B includes or is in optical communication with a second common port 406B and a second reflection port 408B. ln certain embodiments, the two common ports 406A, 406B and the two reflection ports 408A, 408B are associated with the single housing 404. The two common ports 406A, 406B are configured to transmit a “transmission signal” of a multiplexed signal along an optical path therebetween. The two common ports 406A, 406B and the two reflection ports 408A, 408B may each comprise one or more fiber optic connectors, one or more optical splices, one or more optical fibers, free- space, or a combination of the forgoing.

[0042] The first collimator 402A includes a first wave -division multiplexing (WDM) filter 410A having at least one first passband, and the second collimator 402B includes a second WDM filter 410B having at least one second passband. The first and second WDM filters 410A, 410B are positioned in the optical path between the first common port 406A (e.g., first common fiber) and the second common port 406B (e.g., second common fiber). At least a portion of the optical path extending between the first and second WDM filters 410A, 410B is devoid of an optical fiber ln FIG. 4A, for example, the area between the first and second WDM filters 410A, 410B is free-space and is completely devoid of an optical fiber.

[0043] The first WDM filter 410A routes“transmission signals” of multiplexed signals from the first common port 406A through the first WDM filter 410A and towards the second common port 406B and routes“drop demultiplexed signals” of the multiplexed signals from the first common port 406A to the first reflection port 408A (e.g., through the second optical fiber 434A). The second WDM filter 410B routes the “transmission signals” from the multiplexed signals from the first common port 406A through the second WDM filter 410B towards the second common port 406B and routes“add demultiplexed signals” from the second reflection port 408B (e.g., reflection fiber) to the second common port 406B. Accordingly, the OADM device 400 (e.g., a four port OADM device) may provide a number of improvements and advantages, particularly over the three-port TFF device 200 (discussed above with respect to FIGS. 2-4A). ln particular, the OADM device 400 may provide a simpler, more economic, more compact design using fewer components. Further, the OADM device 400 may achieve better optical performance by reducing the number of interfaces required to add and drop demultiplexed signals between the two common ports 406A, 406B. Specifically, by comparison to the assembly 300 of F1G. 3, the OADM device 400 removes the second collimators 204-1, 204-2 (e.g., C-lens and pigtail) of the first and second TFF devices 200-1, 200-2 and condenses the device to a single housing 404.

[0044] Referring again to FIG. 4A, the first collimator 402A (which may also be referred to as a first micro-optical system) includes the first WDM filter 410A, a first collimating lens 412A, a first dual fiber pigtail 414A (may also be referred to as a dual fiber optic pigtail), and a first mounting structure 416A (to mount the first collimator 402 A to the housing 404). The first collimating lens 412A is positioned between the first WDM filter 410A and the first dual fiber pigtail 414A. ln particular, the first WDM filter 410A includes a medial end 418A and a distal end 420A opposite the medial end 418A. The first collimating lens 412A includes a medial end 422A and a distal end 424A opposite the medial end 422A. The first dual fiber pigtail 414A includes a medial end 426A and a distal end 428A opposite the medial end 426A. The distal end 420A of the WDM filter 410A is mounted to (or proximate to) the medial end 422A of the first collimator 402A, the distal end 424A of the first collimator 402A is mounted to (or proximate to) the medial end 426A of the first dual fiber pigtail 414A.

[0045] ln certain embodiments, the first WDM filter 410A is a first thin-film filter (TFF), although other filters can be used ln certain embodiments, the first collimating lens 412A is a G-lens (may also be referred to as a gradient-index (GR1N) lens), although other collimating lenses may be used (e.g., C-lens). The medial end 422A of the first collimator 402A may include a planar surface (such as with a G-lens) to facilitate mounting of the first WDM filter 410A thereto.

[0046] The first dual fiber pigtail 414A includes the first common port 406A and the first reflection port 408A. The first dual fiber pigtail 414A includes a first ferrule 430A secured to the first mounting structure 416A, a first optical fiber 432A (may also be referred to as a first common fiber) having a portion positioned within the ferrule 430A and a fiber end 433A, a second optical fiber 434 A (may also be referred to as a first reflection fiber) having a portion positioned within the ferrule 430A and a fiber end 435A, and a securing element 436A for securing the first and second optical fibers 432A, 434A to the ferrule 430A. The ferrule 430A provides optical fiber support. The first ferrule 430A may be made of ceramic, metal, glass, plastic, etc., depending on the requirements for robustness and/or flexibility. The first optical fiber 432A is in optical communication with the first common port 406A, and the second optical fiber 434A is in optical communication with the first reflection port 408A. The first common port 406A is configured for optical communication of a first multiplexed signal comprising a transmission signal and a first demultiplexed signal. The first reflection port 408A is configured for optical communication of the first demultiplexed signal (after separation from the transmission signal).

[0047] The securing element 436A (e.g., adhesive, a mechanical fastener, etc.) can be disposed around the first and second optical fibers 432A, 434A at the back end of the first ferrule 430 A to secure the optical fibers 432 A, 434A to the ferrule 430A.

[0048] The second collimator 402B (may also be referred to as a first micro-optical system) includes the second WDM filter 410B, a second collimating lens 412B, a second dual fiber pigtail 414B (may also be referred to as a second dual fiber optic pigtail), and a second mounting structure 416B (to mount the first collimator 402A to the housing 404). The second collimating lens 412B is positioned between the second WDM filter 410B and the second dual fiber pigtail 414B. ln particular, the second WDM filter 410B includes a medial end 418B and a distal end 420B opposite the medial end 418B. The second collimating lens 412B includes a medial end 422B and a distal end 424B opposite the medial end 422B. The second dual fiber pigtail 414B includes a medial end 426B and a distal end 428B opposite the medial end 426B. Accordingly, the distal end 420B of the WDM filter 410B is mounted to (or proximate to) the medial end 422B of the second collimating lens 412B, the distal end 424B of the second collimating lens 412B is mounted to (or proximate to) the medial end 426B of the second dual fiber pigtail 414B.

[0049] ln certain embodiments, the second WDM filter 410B is a first thin-film filter (TFF), although other filters can be used ln certain embodiments, the second collimating lens 412B is a G-lens (may also be referred to as a gradient-index (GRIN) lens or G-lens), although other collimating lenses may be used (e.g., C-lens). The medial end 422B of the second collimating lens 412B may include a planar surface (such as with a G-lens) to facilitate mounting of the second WDM filter 410B thereto.

[0050] The second dual fiber pigtail 414B includes the second common port 406B and the second reflection port 408B. The second dual fiber pigtail 414B includes a second ferrule 430B secured to the second mounting structure 416B, a first optical fiber 432B (may also be referred to as a second common fiber) having a portion positioned within the ferrule 430B and a fiber end 433B, a second optical fiber 434B (may also be referred to as a second reflection fiber) having a portion positioned within the ferrule 430B and a fiber end 435B, and a securing element 436B for securing the first and second optical fibers 432B, 434B to the ferrule 430B. The ferrule 430B provides optical fiber support. The second ferrule 430B may be made of ceramic, metal, glass, plastic, etc., depending on the requirements for robustness and/or flexibility. The first optical fiber 432B is in optical communication with the second common port 406B, and the second optical fiber 434B is in optical communication with the second reflection port 408B. The second common port 406B is configured for optical communication of a second multiplexed signal comprising the transmission signal and a second demultiplexed signal. The second reflection port 408B is configured for optical communication of the second demultiplexed signal.

[0051] The securing element 436B (e.g., adhesive, a mechanical fastener, etc.) can be disposed around the first and second optical fibers 432B, 434B at the back end of the second ferrule 430B to secure the optical fibers 432B, 434B to the ferrule 430B.

[0052] The housing 404 has a first end 438A and a second end 438B opposite the first end 438A. The housing defines a first opening 440A at the first end 438A, a second opening 440B at the second end 438B, and an interior 442 therebetween. The housing 404 (e.g., tube) is generally cylindrical with a cross-sectional outer surface of a first shape (e.g., circular, square, etc.) and an inner surface of a second shape (e.g., circular, square, etc.) which may be the same shape as, or different from, the shape of the outer surface ln certain embodiments, the housing 404 is made of metal, ceramic, glass, plastic, etc. The first collimator 402 A is at least partially positioned within the housing 404 at the first end 438A of the housing 404 (e.g., within the first opening 440A) and the second collimator 402B is at least partially positioned within the housing 404 at the second end 438B of the housing 404 (e.g., within the second opening 440B). ln particular, the first collimator 402A is positioned within the first mounting structure 416A, which is positioned within the first opening 440 A and mounted to the housing 404, and the second collimator 402B is positioned within the second mounting structure 416B, which is positioned within the second opening 440B and mounted to the housing 404. ln other words, the first dual fiber pigtail 414A (and the first common port 406A and the first reflection port 408A) is positioned at the first end 438A, and the second dual fiberpigtail 414B (and the second common port 406B and the second reflection port 408B) is positioned at the second end 438B. ln other embodiments, the first and second collimators 402A, 402B are positioned on a substrate in addition to or instead of within a housing 404.

[0053] The first collimator 402A (and the fibers of the first dual fiber pigtail 414A) is generally aligned (but slightly offset) with the second collimator 402B (and the fibers of the second dual fiber pigtail 414B) along axis A-A, and the medial end 418A of the first WDM filter 410A is separated from the medial end 418B of the second WDM filter 410B by free space 444 (e.g., an air gap). Since the output angle of the transmission signal from the medial end 418A of the first WDM filter 410A and the medial end 4118B of the second WDM filter 410B are not normal, the alignment configuration of the first collimator 402A and the second collimator 402B is not symmetric to the axis A-A (i.e., vertically offset). The first collimating lens 412A and the first dual fiber pigtail 414A form an optical path from end faces of the optical fibers 432A, 434A through the first collimating lens 412A and the first WDM filter 410A. Similarly, the second collimating lens 412B and the second dual fiber pigtail 414B form an optical path from end faces of the optical fibers 432B, 434B through the second collimating lens 412B and the second WDM filter 41 OB. The first collimator 402A is in optical communication with the second collimator 402B with an optical path extending through the first WDM filter 410A, across the free space 444, and through the second WDM filter 410B. Thus, the first and second WDM filters 410A, 410B are positioned in an optical path between the first common port 406A and the second common port 406B. lt is noted that there is no optical fiber in the optical path between distal ends 420A, 420B of the first and second WDM filters 410A, 410B.

[0054] The first WDM filter 410 A has a first passband and the second WDM filter 410B has a second passband, which may be the same or different than the first passband. ln certain embodiments, the WDM filters 410A, 410B are attached to the collimating lenses 412A, 412B by laser welding, glass welding, an adhesive (e.g., epoxy, glue, etc.) ln other embodiments, the WDM filters 410A, 410B are not attached to the collimating lenses 412A, 412B, but are otherwise positioned in the optical path.

[0055] FIG. 4B is close up cross-sectional top view of the first and second collimators 402A, 402B of the OADM device 400 of FIG. 4A illustrating dropping and adding signals using two WDM filters 410A, 410B. lt is noted that the first optical fiber 432A of the first dual fiber pigtail 414A is aligned with the second optical fiber 434B of the second dual fiber pigtail 414B, and the second optical fiber 434A of the first dual fiber pigtail 414A is aligned with the first optical fiber 432B of the second dual fiber pigtail 414B. ln FIG. 4B, the dashed lines illustrate schematically the optical paths.

[0056] A first multiplexed signal is transmitted from the first common port 406A through the first optical fiber 432A of the first dual fiber pigtail 414A through the first collimating lens 412A through the WDM filter 410A to the first passband (e.g., single passband, multi- passband, etc.) at the medial end 418A of the first WDM filter 410A (although in some embodiments the passband is at the distal end 420A of the first WDM filter 410A). The multiplexed signal includes a“transmission signal” and a“drop demultiplexed signal.” ln certain embodiments, the transmission signal is a multiplexed signal comprising multiple demultiplexed signals. The first passband of the first WDM filter 410A routes the transmission signal (with a wavelength within the first passband) through the first WDM filter 410A and reflects the drop demultiplexed signal (with a wavelength outside the first passband) back along the first collimating lens 412A to the second optical fiber 434A to the first reflection port 408A.

[0057] The transmission signal is then transmitted from the medial end 418A across the free space 444 to the medial end 418B of the second WDM filter 410B. The second passband at the medial end 418B of the second WDM filter 410B routes the transmission signal (with a wavelength within the second passband) through the second WDM filter 410B. An“add demultiplexed signal” is transmitted from the second reflection port 408B through the second optical fiber 434B of the second dual fiber pigtail 414B through the second collimating lens 412B to the second WDM filter 410B. The second passband of the second WDM filter 410B routes the transmission signal (with a wavelength within the second passband) through the second WDM filter 410B and reflects the add demultiplexed signal (with a wavelength outside the first passband), such that the transmission signal and the add demultiplexed signal form a second multiplexed signal. The second multiplexed signal is transmitted along the second collimating lens 412B to the second optical fiber 434B of the second dual fiber pigtail 414B to the second common port 406B.

[0058] ln other words, the first WDM filter 410A is configured to route the first demultiplexed signal of the first multiplexed signal from the first common port 406A to the first reflection port 408A, and the transmission signal from the first common port 406A to the second common port 406B. The second WDM filter 410B is configured to route the transmission signal from the first common port 406A to the second common port 406B, and the second demultiplexed signal from the second reflection port 408B to the second common port 406B to at least partially form the second multiplexed signal.

[0059] The OADM device 400 operates similarly in the reverse ln other words, if a multiplexed signal is sent from the second common port 406B of the second collimator 402B to the first common port 406A of the first collimator 402A, then the second reflection port 408B receives drop demultiplexed signals, and the first reflection port 408A transmits add demultiplexed signals.

[0060] Such a configuration provides the same functionality as the three-port TFF assembly 300 of FIG. 3, with fewer components, a reduced footprint, and fewer optical couplings. Optical couplings occur between components of each collimator 402A, 402B and between collimators (e.g., across the free space 444). For example, the three-port TFF assembly 300 of FIG. 3 includes about ten optical couplings (between component interfaces), while the OADM device 400 of FIGS. 4A-4B includes only about six optical couplings. Accordingly, the OADM device FIGS. 4A-4B also results in reducing signal loss and improved signal performance.

[0061] FIG. 5 is a cross-sectional top view of an OADM assembly 500 with two OADM devices 400-1, 400-2 of FIGS. 4A-4B connected in series (e.g., by fiber fusion-splicing, optical connector, epoxy curing, etc.) ln particular, the second common port 406B-1 of the first OADM device 400-1 is optically connected, for example, by an optical fiber with the first common port 406A-2 of the second OADM device 400-2. Of course, the OADM device 500 could include additional OADM devices 400, and/or other devices (e.g., three-port TFF device).

[0062] FIGS. 6-9 illustrate alternative configurations of the OADM device 400 of FIGS. 4A-4B. ln particular, FIGS. 6-7 illustrate configurations of the OADM device 400 without the collimating lens, such as in applications where there is no need for beam focus.

[0063] FIG. 6 is a top view of another embodiment of the OADM device 400 of FIGS. 4A-4B, where the OADM device 600 includes two WDM filters 410A, 410B attached respectively to two dual fiber pigtails 414A, 414B and separated by free space 444. The OADM device 600 omits the collimating lenses 412A, 412B of FIGS. 4A-4B for a more compact design. Further, the WDM filters 410A, 410B are attached respectively to medial ends 426A, 426B of dual fiber pigtails 414A, 414B by an attachment layer 602A, 602B. ln certain embodiments, the attachment layer 502A, 502B includes an adhesive (e.g., glue, epoxy, etc.) ln certain embodiments, the WDM filters 410A, 410B are attached to the ferrule 430A, 430B of the dual fiber pigtails 414A, 414B by laser welding, glass welding, etc. ln certain embodiments, the attachment layer 502A, 502B includes functional materials to manage beam shape, intensity (e.g., reduce signal intensity loss), energy, traveling quality (e.g., improve traveling quality), and/or spectrum ln other embodiments, the WDM filters 410A, 410B are not attached to the dual fiber pigtails 414A, 414B but are otherwise positioned in the optical path.

[0064] FIG. 7 is a top view of another embodiment of the OADM device 600 of FIG. 6, where the OADM device 700 includes with two WDM filters 410A, 410B attached respectively to two dual fiber pigtails 414A, 414B and separated by an intermediate layer 702, such as an index-matching material (e.g., index-matching epoxy, index-matching gel, etc.) ln some embodiments, the intermediate layer 602 contacts and extends between medial ends 418A, 418B of the two WDM filters 410A, 410B. ln this way, the intermediate layer 602 reduces (or eliminates) refraction and/or reduces optical intensity loss as the transmission signal transmits between the two WDM filters 410A, 410B.

[0065] FIG. 8 is a top view of another embodiment of the OADM device 400 of FIGS. 4A-4B, where the OADM device 800 includes two WDM filters 410A, 410B attached respectively to two dual fiber pigtails 414A, 414B and the two WDM filters 410A, 410B abut or contact each other ln other words, the medial ends 418A, 418B of the two WDM filters 410A, 410B abut each other such that there is substantially no free space 444 (i.e., air gap) in between the two WDM filters 410A, 410B. This provides a more compact design and may improve optical performance by decreasing loss.

[0066] FIG. 9 is a top view of another embodiment of the OADM device 400 of FIGS. 4A-4B, where the OADM device 900 includes a single WDM filter 902 attached to two dual fiber pigtails 414A, 414B. Such a configuration may provide the same functionality as that described with respect to the OADM device 400 of FIGS. 4A-4B. ln particular, the transmission signal of the multiplexed signal is transmitted between the first and second common ports 406A, 406B through the WDM filter 902. When the transmission signal is transmitted from the first common port 406A of the first dual fiber pigtail 414A to the second common port 406B of the second dual fiber pigtail 414B, the first reflection port 408A receives drop demultiplexed signals, and the second reflection port 408B transmits add demultiplexed signals. Even with only one WDM filter 902, the drop demultiplexed signals are dropped from the first multiplexed signal transmitted through the first optical fiber 432A of the first dual fiber pigtail 414A and the add demultiplexed signals are added to form the second multiplexed signal transmitted through the first optical fiber 432B of the second dual fiber pigtail 414B. This is because a first side 904A of the WDM filter 902 reflects the drop demultiplexed signal, and a second side 904B of the WDM filter 902 reflects the add demultiplexed signal, such that the drop demultiplexed signals and the add demultiplexed signals are isolated from one another.

[0067] FIGS. 10A-10C are views of WDM filters for use with the OADM devices of FIGS. 4A-8. ln particular, FIG. 10A is a side view of a WDM filter 1000 including a dielectric layer 1002 and a glass substrate 1004. The glass substrate includes a first side 1006A and a second side 1006B opposite the first side 1006A. The dielectric layer 1002 is deposited on the first side 1006A. FIG. 10B is a side view of a WDM filter 1008 including two dielectric layers 1002A, 1002B deposited on opposing sides 1006A, 1006B of a glass substrate 1004. FIG. 10C is a side view of a WDM filter 1010 including one dielectric layer 1002 without a glass substrate. Removing the glass substrate provides a much thinner WDM filter 1010. ln certain embodiments, the WDM filter 1010 is coated (or otherwise deposited) on the collimating lens and/or pigtail (e.g., ferrule). For example, the dielectric layer 1002 of a thin-film filter can be coated onto the front surface of a pigtail. This is because the typical Rayleigh range of a divergent optical beam (e.g., around a few tens of micrometers in fiber optical communication industry) is far less than the thickness of the dielectric layer 1002 (e.g., in the order of millimeter or sub-millimeter). Removing the glass substrate provides accurate control of signal spectrum by minimizing the distance between two transmitting components ln certain embodiments, other techniques are used that generate thin film with dielectric layers only for optical signal management in either wavelength or intensity. For example, some techniques peel the dielectric layers off the substrate so that the layer(s) can be inserted in between two pigtails, such as shown in FIGS. 8-9.

[0068] FIG. 11 is a top view of a non-linear arrangement of the first and second dual fiber pigtails of the OADM device of FIG. 6. However, this arrangement could be used with any of the OADM devices of FIGS. 4A-9. The OADM device 1100 includes the first and second dual fiber pigtails 414A, 414B (along with the WDM filters 410A, 410B) illustrated in FIG. 6 angularly offset from each other (at a non-zero angle) ln other words, the first dual fiber pigtail 414A is aligned along a first axis B-B, and the second dual fiber pigtail 414B is aligned along a second axis C-C, where the first axis B-B is non-parallel to the second axis C-C (e.g., perpendicular to one another). Further, the first axis B-B and the second axis C-C intersect an optical signal router 1102 (e.g., mirror, prism, lens, etc.) ln this way, the optical signal router 1102 forms an optical path between the first common port 406A of the first dual fiber pigtail 414A and the second common port 406B of the second dual fiber pigtail 414B.

[0069] Of course, in other embodiments, the first and second dual fiber pigtails 414A, 414B may be offset but parallel to one another (i.e., not aligned along a common axis), with an optical signal router 1102 to route an optical path between the first commonport 406A of the first dual fiber pigtail 414A and the second common port 406B of the second dual fiber pigtail 414B.

[0070] FIG. 12A is a flowchart of steps 1200 for manufacturing an OADM optical device of FIGS. 4A-9. For aligning two WDM filters, in step 1202, a first WDM filter 410A having a first passband is positioned to align a first common port 406A (see FIGS. 4A-4B) with a first reflection port 408A (see FIGS. 4A-4B) for optical communication of a first demultiplexed signal (e.g.,“drop demultiplexed signal”) of a first multiplexed signal ln step 1204, a second WDM filter 410B having a second passband is positioned to align a second commonport 406B (see FIGS. 4A-4B) with a second reflection port 408B (see FIGS. 4A-4B) for optical communication of a second demultiplexed signal (e.g.,“add demultiplexed signal”) to form a second multiplexed signal with a transmission signal of the first multiplexed signal ln step 1206, the first common port 406A and the second common port 406B are aligned with each other for optical communication of the transmission signal of the first multiplexed signal therebetween ln this way, the WDM filters 410A, 410B are positioned in an optical path between the first common port 406A and the second common port 406B for routing the transmission signal, the first demultiplexed signal, and the second demultiplexed signal. The WDM filters 410A, 410B each have a first side and a second side opposite the first side. A portion of the optical path extending between the first side and the second side of the WDM filters 410A, 410B is devoid of an optical fiber ln particular, the WDM filters 410A, 410B are configured to route (i) the first demultiplexed signal of the first multiplexed signal from the first common port 406A to the first reflection port 408A, (ii) the transmission signal from the first common port 406A to the second common port 406B, and (iii) the second demultiplexed signal from the second reflection port 408B to the second common port 406B to at least partially form the second multiplexed signal.

[0071] Alternatively, in the case of using only one WDM filter, step 1204 is omitted, and instead after step 1206 the second reflection port 408B is aligned with the second common port 406B, while maintaining alignment of the first common port 406A with the second common port 406B.

[0072] FIG. 12B is a flowchart of steps 1208 for using an OADM optical device of FIGS. 4A-9. ln step 1210, a first common port 406A (see FIGS. 4A-4B) transmits a first multiplexed signal including a transmission signal and a first demultiplexed signal ln step 1212, a first WDM filter 410A (see FIGS. 4A-4B) routes the first demultiplexed signal of the first multiplexed signal from the first common port 406A of a first dual fiber pigtail 414A (see FIGS. 4A-4B) to a first reflection port 408A of the first dual fiber pigtail 414A and transmits the transmission signal toward a second common port 406B (see FIGS. 4A-4B). ln step 1214, a second WDM filter 410B (see FIGS. 4A-4B) routes a second demultiplexed signal from a second reflection port 408B of a second dual fiber pigtail 414B to a second common port 406B of the second dual fiber pigtail 414B (see FIGS. 4A-4B) such that the second demultiplexed signal and the transmission signal form a second multiplexed signal and transmits the second multiplexed signal to the second common port 406B.

[0073] FIGS. 13-15B are views of example collimators for use with the components and devices of FIGS. 4A-11.

[0074] FIG. 13 is a perspective view of an example steel-tube collimator 1300 for use with the OADM devices and assemblies of FIGS. 4A-11. The collimator narrows a beam of particles or waves ln other words, the collimator causes the directions of motion to become more aligned in a specific direction. The steel-tube collimator 1300 includes a steel-tube body 1302, with a curved lens 1304 at one end of the steel-tube body, and a fiber optic pigtail 1306 at an opposite end of the steel-tube body.

[0075] FIGS. 14A and 14B are perspective and cross-sectional views, respectively, of an example square tube collimator for use with the OADM devices and assemblies of FIGS. 4A- 11. The square tube collimator 1400 includes a glass tube 1402 (e.g., cylindrical) with a central bore 1404. As used herein, the term“cylindrical” is used in its most general sense and can be defined as a three-dimensional object formed by taking a two-dimensional object and projecting it in a direction perpendicular to its surface. Thus, a cylinder, as the term is used herein, is not limited to having a circular cross-section shape but can have any cross-sectional shape, such as the square cross-sectional shape described below by way of example.

[0076] The square tube collimator 1400 further includes optical elements, such as a collimating lens 1406, ferrule 1408, etc., which can be secured to the glass tube 1402 using a securing mechanism (e.g., an adhesive). The collimating lens 1406 has a front surface 1410A and a back surface 1410B opposite thereto ln the example shown, the front surface 1410A is convex while the back surface 1410B can be angled, e.g., in the x-z plane as shown ln an example, the front surface 1410A of collimating lens 1406 can reside outside of the central bore 1404, i.e., the front-end portion of the collimating lens 1406 can extend slightly past the front end of the glass tube 1402. ln an example, the collimating lens 1406 can be formed as a gradient-index (GRJN) element that has a planar front surfacel410A. ln an example, the collimating lens 1406 can consist of a single lens element, while in another example it can consist of multiple lens elements ln the discussion below, the collimating lens 1406 is shown as a single lens element for ease of illustration and discussion.

[0077] The optical fiber support member is the form of a ferrule 1408. The ferrule 1408 includes a central bore 1412 that runs between a front end and aback end along a ferrule central axis AF, which in an example is co-axial with the tube central axis AT of the glass tube 1402 and the optical axis OA as defined by the collimating lens 1406. The central bore 1412 can include a flared portion 1414 at the back end of the ferrule 1408.

[0078] An optical fiber 1416 has a coated portion 1418, and an end portion 1420 is bare glass (e.g., is stripped of the coated portion) and is thus referred to as the“bare glass portion.” The bare glass portion 1420 includes a polished end face 1422 that defines a proximal end of the optical fiber. The bare glass portion 1420 of the optical fiber 1416 extends into the central bore 1412 of the ferrule 1408 at the back end of the ferrule. A securing element 1424 can be disposed around the optical fiber 1416 at the back end of the ferrule 1408 to secure the optical fiber to the ferrule. The front end of the ferrule 1408 is angled in the x-z plane and is axially spaced apart from the angled back end of the collimating lens to define a gap 1426 that has a corresponding axial gap distance DG. While a glass optical fiber is described above, other types of optical fibers may be used, such as, for example, a plastic optical fiber.

[0079] The ferrule 1408, optical fiber 1416, and securing element 1424 constitute a fiber optic pigtail 1428, which can be said to reside at least partially within the bore 1404 adjacent the back end of the glass tube 1402. Thus, in an example, the square tube collimator 1400 includes only the glass tube 1402, the collimating lens 1406, and the fiber optic pigtail 1428. The glass tube 1402 serves in one capacity as a small lens barrel that supports and protects the collimating lens 1406 and fiber optic pigtail 1428, particularly the bare glass portion 1420 and its polished end face 1422. The glass tube 1402 also serves in another capacity as a mounting member that allows for the square tube collimator 1400 to be mounted to a support substrate ln this capacity, at least one flat surface 1430 serves as a precision mounting surface.

[0080] ln an example, the glass tube 1402, the collimating lens 1406, and the ferrule 1408 are all made of a glass material, and further in an example, are all made of the same glass material. Making the glass tube 1402, the collimating lens 1406, and the ferrule 1408 out of a glass material has the benefit that these components will have very close if not identical coefficients of thermal expansion (CTE). This feature is particularly advantageous in environments that can experience large swings in temperature.

[0081] ln an example, the optical elements used in micro-optical systems are sized to be slightly smaller than the diameter of the bore 1404 (e.g., by a few microns or tens of microns) so that the optical elements can be inserted into the bore 1404 and be movable within the bore 1404 to a select location ln an example, the select location is an axial position where the optical element resides for the micro-optical system to have optimum or substantially optimum optical performance. Here, substantially optimum performance means performance that may not be optimum but that is within a performance or specification for the micro-optical system.

[0082] ln another example, the optical elements have a clearance with respect to the bore 1404 in the range of a few microns (e.g., 2 microns or 3 microns) to tens of microns (e.g., 20 microns up to 50 microns). A relatively small value for the clearance allows for the optical elements to be well-aligned with the central bore axis AB, e.g., to within a few microns (e.g., from 2 microns to 5 microns).

[0083] The optical elements and the support/positioning elements can be inserted into and moved within the bore 1404 to their select locations using micro-positioning devices. The optical elements and the support/positioning elements can be secured within the bore 1404 using a number of securing techniques. One example of a securing technique uses a securing feature that is an adhesive (e.g., a curable epoxy). Another securing technique uses a securing feature that involves a glass soldering to create one or more glass solder points. Another securing technique uses glass welding to create a securing feature in the form of one or more glass welding points. A combination of these securing features can also be employed.

[0084] Thus, one or more optical elements can be secured within the bore 1404 using one or more securing features, and can also be supported and/or positioned using one or more support/positioning elements. The non-adhesive securing techniques described below allow for the micro-optical systems disclosed herein to remain free of adhesives so that, for example, micro-optical systems can consist of glass only.

[0085] FIG. 15A is a side view of an example compact collimator for use with the OADM devices and assemblies of FIGS. 4A-11. The collimator 1500 includes a lens 1502 (e.g., a glass or silica collimating lens), a fiber optic pigtail 1504, and a groove (e.g., a generally V- shaped groove) formed in a base 1506. The lens 1502 and the fiber optic pigtail 1504 are disposed in the groove. The lens 1502 is configured to receive a light signal provided to the WDM multiplexer/demultip lexer from an external optical transmission system or provide a light signal multiplexed or demultiplexed by the WDM to an external optical transmission system. The lens 1502, for example, may be configured to receive a light signal from a fiber optic element for multiplexing or demultiplexing and/or to provide a multiplexed or demultiplexed light signal to an external fiber optic element. The fiber optic pigtail 1504 is optically coupled to the lens 1502 and is configured to provide a light signal to the lens 1502 from the external fiber optic element and/or to receive the light signal from the lens 1502 for transmission to the external fiber optic element.

[0086] ln various embodiments, the lens 1502 and the fiber optic pigtail 1504 may or may not contact each other. The lens 1502 and the fiber optic pigtail 1504 may be securable to the groove independent of each other to allow for precise adjustment of a pointing angle between an optical beam from the collimator 1500 and a side and/or bottom surface of the groove ln addition, the lens 1502 and fiber optic pigtail 1504 may have the same outer diameter.

[0087] The base 1506 of the collimator 1500 has a generally flat bottom surface 1508 for mounting on a substrate of a WDM multiplexer/demultip lexer or other optical system. The base 1506 further includes a width that is less than a width of the lens 1502 and a width of the fiber optic pigtail 1504. [0088] FIG. 15B is a close-up side view of the compact collimator of FIG. 15A. A pointing angle between an optical beam from a collimator 1500 and the side and bottom surface of the groove can be eliminated (or at least reduced) by controlling the relative position between the lens 1502 and the fiber optic pigtail 1504 of the collimator 1500. By fine tuning the position of the fiber optic pigtail 1504 to make an outgoing beam come across a focal point of the lens 1502, a collimated zero pointing angled beam with negligible off axis offset can be achieved ln one embodiment, for example, the tuning can be monitored by near field and far field beam position comparison (e.g., using a beam scanner). The zero pointing angle collimating components are easier to attach to the substrate with little inclination, and more reliable bonding is possible due to the uniform epoxy or bonding agent lt is noted that FIG. 14B is a schematic illustration used to illustrate concepts of the description, and that the ends of the glass lens and the fiber optic pigtail 1504 may be oriented at other angles, including perpendicular, to the body of the glass lens and the fiber optic pigtail, respectively.

[0089] lt will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention.

[0090] Further, as used herein, it is intended that terms“fiber optic cables” and/or“optical fibers” include all types of single mode and multi-mode light waveguides, including one or more optical fibers that maybe glass core, plastic core, upcoated, colored, buffered, ribbonized and/or have other organizing or protective structure in a cable such as one or more tubes, strength members, jackets or the like. Likewise, other types of suitable optical fibers include bend-insensitive optical fibers, or any other expedient of a medium for transmitting light signals. An example of a bend-insensitive, or bend resistant, optical fiber is ClearCurve^® Multimode fiber commercially available from Coming lncorporated. Suitable fibers of this type are disclosed, for example, in U.S. Patent Application Publication Nos. 2008/0166094 and 2009/0169163.

[0091] Many modifications and other embodiments of the embodiments set forth herein will come to mind to one skilled in the art to which the embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the description and claims are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is intended that the embodiments cover the modifications and variations of the embodiments provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

What is claimed is:

1. An optical add-and-drop multiplexer (OADM) device, comprising:

a first dual fiber pigtail at least partially positioned within a housing, the first dual fiber pigtail comprising a first common fiber and a first reflection fiber, the first common fiber configured for optical communication of a first multiplexed signal comprising a transmission signal and a first demultiplexed signal, the first reflection fiber configured for optical communication of the first demultiplexed signal;

a second dual fiber pigtail at least partially positioned within the housing, the second dual fiber pigtail comprising a second common fiber and a second reflection fiber, the second common fiber configured for optical communication of a second multiplexed signal comprising the transmission signal and a second demultiplexed signal, the second reflection fiber configured for optical communication of the second demultiplexed signal; and

at least one wave-division multiplexing (WDM) filter having a passband;

wherein the at least one WDM filter is configured to route (i) the first demultiplexed signal of the first multiplexed signal from the first common fiber to the first reflection fiber, (ii) the transmission signal from the first common fiber to the second common fiber, and (iii) the second demultiplexed signal from the second reflection fiber to the second common fiber.

2. The OADM device of claim 1, wherein the housing comprises a first opening and a second opening opposite the first opening, the first dual fiber pigtail positioned at the first opening and the second dual fiber pigtail positioned at the second opening.

3. The OADM device of either of claims 1 or 2,

wherein the at least one WDM filter comprises a first WDM filter and a second WDM filter;

wherein the first WDM filter is configured to route (i) the first demultiplexed signal of the first multiplexed signal from the first common fiber to the first reflection fiber, and (ii) the transmission signal from the first common fiber to the second common fiber; and wherein the second WDM filter is configured to route (i) the transmission signal from the first common fiber to the second common fiber, and (ii) the second demultiplexed signal from the second reflection fiber to the second common fiber.

4. The OADM device of claim 3, wherein the first WDM filter is separated from the second WDM filter by a free space.

5. The OADM device of claim 3, wherein the first WDM filter contacts the second WDM filter.

6. The OADM device of claim 3, further comprising an intermediate layer between the first WDM filter and the second WDM filter.

7. The OADM device of claim 6, wherein the intermediate layer comprises an index matching material.

8. The OADM device of any of claims 1-7, wherein the first dual fiber pigtail comprising a first ferrule and the first common fiber and the first reflection fiber extend from the ferrule.

9. The OADM device of claim 8, wherein the first common fiber comprises a first common port and the first reflection fiber comprises a first reflection port, wherein the first common port and the first reflection port each comprise a fiber optic connector.

10. The OADM device of any of claims 1-9,

wherein the first dual fiber pigtail comprises a first ferrule; and

wherein the at least one WDM filter is attached to a surface of the first ferrule.

11. The OADM device of any of claims 1-10,

wherein the first dual fiber pigtail comprises a first ferrule; and

wherein the at least one WDM filter is coated onto a surface of the ferrule.

12. The OADM device of any of claims 1-11, wherein the first dual fiber pigtail is aligned with the second dual fiber pigtail along a central axis of the housing.

13. The OADM device of any of claims 1-12, wherein the first dual fiber pigtail is offset from the second dual fiber pigtail.

14. The OADM device of claim 13, further comprising an optical signal router positioned to route optical signals from the first dual fiber pigtail to the second dual fiber pigtail.

15. An optical add-and-drop multiplexer (OADM) device, comprising:

a housing comprising a first common port, a first reflection port, a second common port, and a second reflection port; and

at least one wave-division multiplexing (WDM) filter having a passband, wherein the at least one WDM filter is configured to route (i) a first demultiplexed signal of a first multiplexed signal from the first common port to the first reflection port, (ii) a transmission signal from the first common port to the second common port, and (iii) a second demultiplexed signal from the second reflection port to the second common port to at least partially form a second multiplexed signal.

16. The OADM device of claim 15, further comprising a first dual fiber pigtail comprising the first common port and the first reflection port, and a second dual fiber pigtail comprising the second common port and the second reflection port.

17. The OADM device of claim 16, further comprising a housing having a first opening and a second opening opposite the first opening, the first dual fiber pigtail at least partially located in the first opening and the second dual fiber pigtail at least partially located in the second opening.

18. The OADM device of claim 17, wherein the first dual fiber pigtail is aligned with the second dual fiber pigtail along a central axis of the housing.

19. The OADM device of claim 17, wherein the first dual fiber pigtail is offset from the second dual fiber pigtail.

20. The OADM device of any of claims 16-19,

wherein the first dual fiber pigtail comprises a first ferrule; and wherein the at least one WDM filter is attached to a surface of the first ferrule by an adhesive, glass welding, or laser welding.

21. The OADM device of any of claims 16-20,

wherein the first dual fiber pigtail comprises a first ferrule; and

wherein the at least one WDM filter is coated onto a surface of the ferrule.

22. The OADM device of any of claims 16-21 ,

wherein the first WDM filter is configured to route (i) the first demultiplexed signal of the first multiplexed signal from the first common port to the first reflection port, and (ii) the transmission signal from the first common port to the second common port; and

wherein the second WDM filter is configured to route (i) the transmission signal from the first common port to the second common port, and (ii) the second demultiplexed signal from the second reflection port to the second common port to at least partially form the second multiplexed signal.

23. The OADM device of claim 22, wherein the first WDM filter is separated from the second WDM filter by a free space.

24. The OADM device of either of claims 22 or 23, wherein the first WDM filter contacts the second WDM filter.

25. The OADM device of claim 22, further comprising an intermediate layer between the first WDM filter and the second WDM filter.

26. A method of using an optical add-and-drop multiplexer (OADM) device, comprising: transmitting from a first common port of a first dual fiber pigtail a first multiplexed signal comprising a transmission signal and a first demultiplexed signal;

routing using a first WDM filter the first demultiplexed signal of the first multiplexed signal from the first common port to a first reflection port of the first dual fiber pigtail and transmitting the transmission signal toward a second common port of a second dual fiber pigtail;

routing using a second WDM filter a second demultiplexed signal from a second reflection port of the second dual fiber pigtail to the second common port of the second dual fiber pigtail such that the second demultiplexed signal and the transmission signal form a second multiplexed signal.