IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 12, NO. 5, MAY 2000
`
`561
`
`Bidirectional Wavelength Add–Drop Multiplexer
`Using Multiport Optical Circulators and Fiber Bragg
`Gratings
`
`Jungho Kim and Byoungho Lee, Member, IEEE
`
`Abstract—We propose and experimentally demonstrate a new
`structure of bidirectional wavelength add–drop multiplexer using
`multiport optical circulators and fiber Bragg gratings. It has the
`sufficient suppression of the unwanted light caused by Rayleigh
`backscattering and optical reflection and is economical for the ef-
`fective use of multiport optical circulators.
`Index Terms—Add–drop multiplexer, bidirectional
`trans-
`mission, fiber gratings, optical networks, wavelength-division
`multiplexing.
`
`I. INTRODUCTION
`
`T HE EXPLOSIVE growth of data traffic drives the de-
`
`ployment of wavelength-division-multiplexing (WDM)
`technology. Single fiber bidirectional ring networks (SFBRN’s)
`attract a great deal of attention due to their cost-effectively
`enhanced capacity and possibility of self-healing character-
`istic [1]. A bidirectional wavelength add–drop multiplexer
`(B-WADM) is one of the important components to implement
`SFBRN’s. Several different structures of B-WADM using a
`WDM multiplexer/demultiplexer or an arrayed-waveguide
`grating (AWG) have been proposed and demonstrated [2]–[4].
`In this paper, we propose a reconfigurable B-WADM using
`multiport optical circulators (OC’s) and fiber Bragg gratings
`(FBG’s). The proposed B-WADM has a good filtering shape
`and sufficiently suppresses the relative intensity noise (RIN)
`caused by Rayleigh backscattering and optical
`reflection
`owing to the filtering characteristic of FBG’s. In addition, it is
`cost-effective because it makes an effective use of multiport
`OC’s.
`
`II. CONFIGURATION OF B-WADM
`Fig. 1(a) shows the schematic diagram of the proposed
`B-WADM that can switch three optical channels in each
`direction. The reflective center wavelength of
`the FBG
`i (i = 1; 2; . . . ; N ) is designed to match the optical channel
`i. Three optical channels in each direction enter port 2 of
`each six-port OC, and they are reflected by their corresponding
`FBG’s that are connected to port 3 of the six-port OC. If
`these gratings are chirped, they can simultaneously provide
`
`Manuscript received December 14, 1999; revised February 1, 2000. This
`work was supported in part by the Ministry of Science and Technology of
`Korea through Korea Telecom and KAIST.
`The authors are with the School of Electrical Engineering, Seoul National
`University, Seoul 151-742, Korea (e-mail: byoungho@plaza.snu.ac.kr).
`Publisher Item Identifier S 1041-1135(00)03597-7.
`
`1041–1135/00$10.00 © 2000 IEEE
`
`(a)
`
`(b)
`
`(a) Schematic diagram of the proposed B-WADM that can switch three
`Fig. 1.
`optical channels in each direction. (VA: variable attenuator.) (b) Schematic
`diagram of the proposed B-WADM that can switch only one optical channel
`in each direction.
`
`dispersion compensation for the reflected optical channels.
`Because only two FBG’s are connected to port 4 of the OC,
`one optical channel passes through two FBG’s and enters a
`2 2 optical switch (OSW). The other two optical channels
`are reflected again by their respective FBG’s and sent to the
`next port of the OC. In the same manner, other optical channels
`are separated and enter a 2 2 OSW, respectively. A 2 2
`OSW decides the operation state between “pass through” and
`“add–drop” of each optical channel. Optical channels leaving
`each 2 2 OSW (“pass through” or “added” channels) are
`combined by a 1 N coupler and exit the B-WADM through
`the other six-port OC. If a wavelength multiplexer (MUX)
`replaces a 1 N coupler, it reduces the insertion loss but adds
`cost to the system. Erbium-doped fiber amplifiers (EDFA’s)
`for compensating the loss of the module and the fiber link and
`optical attenuators for optical power equalization are inserted
`in the B-WADM.
`Capella 2013
`Cisco v. Capella
`IPR2014-01166
`
`
`
`561
`
`Bidirectional Wavelength Add–Drop Multiplexer
`Using Multiport Optical Circulators and Fiber Bragg
`Gratings
`
`Jungho Kim and Byoungho Lee, Member, IEEE
`
`Abstract—We propose and experimentally demonstrate a new
`structure of bidirectional wavelength add–drop multiplexer using
`multiport optical circulators and fiber Bragg gratings. It has the
`sufficient suppression of the unwanted light caused by Rayleigh
`backscattering and optical reflection and is economical for the ef-
`fective use of multiport optical circulators.
`Index Terms—Add–drop multiplexer, bidirectional
`trans-
`mission, fiber gratings, optical networks, wavelength-division
`multiplexing.
`
`I. INTRODUCTION
`
`T HE EXPLOSIVE growth of data traffic drives the de-
`
`ployment of wavelength-division-multiplexing (WDM)
`technology. Single fiber bidirectional ring networks (SFBRN’s)
`attract a great deal of attention due to their cost-effectively
`enhanced capacity and possibility of self-healing character-
`istic [1]. A bidirectional wavelength add–drop multiplexer
`(B-WADM) is one of the important components to implement
`SFBRN’s. Several different structures of B-WADM using a
`WDM multiplexer/demultiplexer or an arrayed-waveguide
`grating (AWG) have been proposed and demonstrated [2]–[4].
`In this paper, we propose a reconfigurable B-WADM using
`multiport optical circulators (OC’s) and fiber Bragg gratings
`(FBG’s). The proposed B-WADM has a good filtering shape
`and sufficiently suppresses the relative intensity noise (RIN)
`caused by Rayleigh backscattering and optical
`reflection
`owing to the filtering characteristic of FBG’s. In addition, it is
`cost-effective because it makes an effective use of multiport
`OC’s.
`
`II. CONFIGURATION OF B-WADM
`Fig. 1(a) shows the schematic diagram of the proposed
`B-WADM that can switch three optical channels in each
`direction. The reflective center wavelength of
`the FBG
`i (i = 1; 2; . . . ; N ) is designed to match the optical channel
`i. Three optical channels in each direction enter port 2 of
`each six-port OC, and they are reflected by their corresponding
`FBG’s that are connected to port 3 of the six-port OC. If
`these gratings are chirped, they can simultaneously provide
`
`Manuscript received December 14, 1999; revised February 1, 2000. This
`work was supported in part by the Ministry of Science and Technology of
`Korea through Korea Telecom and KAIST.
`The authors are with the School of Electrical Engineering, Seoul National
`University, Seoul 151-742, Korea (e-mail: byoungho@plaza.snu.ac.kr).
`Publisher Item Identifier S 1041-1135(00)03597-7.
`
`1041–1135/00$10.00 © 2000 IEEE
`
`(a)
`
`(b)
`
`(a) Schematic diagram of the proposed B-WADM that can switch three
`Fig. 1.
`optical channels in each direction. (VA: variable attenuator.) (b) Schematic
`diagram of the proposed B-WADM that can switch only one optical channel
`in each direction.
`
`dispersion compensation for the reflected optical channels.
`Because only two FBG’s are connected to port 4 of the OC,
`one optical channel passes through two FBG’s and enters a
`2 2 optical switch (OSW). The other two optical channels
`are reflected again by their respective FBG’s and sent to the
`next port of the OC. In the same manner, other optical channels
`are separated and enter a 2 2 OSW, respectively. A 2 2
`OSW decides the operation state between “pass through” and
`“add–drop” of each optical channel. Optical channels leaving
`each 2 2 OSW (“pass through” or “added” channels) are
`combined by a 1 N coupler and exit the B-WADM through
`the other six-port OC. If a wavelength multiplexer (MUX)
`replaces a 1 N coupler, it reduces the insertion loss but adds
`cost to the system. Erbium-doped fiber amplifiers (EDFA’s)
`for compensating the loss of the module and the fiber link and
`optical attenuators for optical power equalization are inserted
`in the B-WADM.
`Capella 2013
`Cisco v. Capella
`IPR2014-01166
`
`
`
`562
`
`IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 12, NO. 5, MAY 2000
`
`Fig. 2. Experimental setup of the proposed B-WADM. (TLS: Tunable light
`source.)
`
`the RIN
`transmission system,
`In a general bidirectional
`induced by Rayleigh backscattering and optical reflection may
`degrade the receiver sensitivity. In addition, the maximum gain
`of the optical amplifier used in a bidirectional transmission
`system is limited by the multiple path reflection noise caused
`by Rayleigh backscattering and optical reflection. However,
`in our proposed B-WADM, these effects can be suppressed
`sufficiently by using FBG’s. When the counterpropagating
`optical channels are in different wavelengths, the unwanted
`optical signals induced by Rayleigh backscattering and optical
`reflection pass through the FGB’s that are connected to port 3
`of a six-port OC and are filtered out by a light absorber.
`In the proposed B-WADM, the six-port OC with corre-
`sponding FBG’s can be regarded as a wavelength demultiplexer
`(DEMUX). Compared with conventional DEMUX such as
`an AWG and a multilayer interference-filter-based filter, this
`DEMUX has the good filtering shape that is ascribed to the
`filtering characteristics of FBG. Furthermore, because two
`six-port OC’s simultaneously include the function of separating
`two unidirectional transmission optical signals from the bidi-
`rectional transmission optical signals, we do not need dummy
`three-port OC’s used in the previous structures [3], [4].
`The proposed B-WADM has good design flexibility. Fig. 1(b)
`shows the schematic diagram of the proposed B-WADM that
`can switch only one optical channel in each direction. The
`FBG’s and light absorber that are connected to port 4 of a
`six-port OC suppress the unwanted optical signals induced
`by Rayleigh backscattering and optical reflection. If a 2 2
`OSW is in bar state, all optical channels pass through. Only
`one optical channel whose wavelength matches with the FBG
`can be dropped or added when a 2 2 OSW is in cross-state.
`Compared with the structures of B-WADM using a WDM
`multiplexer/demultiplexer or an AWG, it may be the fittest for a
`B-WADM node that switches only one optical channel because
`it has a low insertion loss and a low cost.
`
`III. EXPERIMENTAL RESULTS
`Fig. 2 shows the experimental setup. Since the configuration
`of the proposed B-WADM is symmetric and there is no mutual
`influence between counterpropagating signals in the system, we
`perform experimental demonstration on only one side of the
`B-WADM. The average insertion loss of a six-port OC (E-Tek
`PIFC2610TER01) is 1.0 dB, and the isolation between adjacent
`ports of the OC’s is >50 dB, respectively. The 2 2 OSW’s
`used here are optomechanical switches with an insertion loss of
`0.7 dB and a crosstalk of <