JP3996749B2 - Optical add / drop device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical add / drop device for dropping an arbitrary wavelength component from a plurality of signal light wavelengths and inserting an arbitrary wavelength component into a signal light.
[0002]
[Prior art]
In the field of wavelength division multiplexing (WDM) optical communication, optical add / drop multiplexers that add / drop arbitrary wavelength components from signal light and add arbitrary wavelength components to signal light have attracted attention. What is disclosed in ““ Optical ADM Experiment Using Fiber Grating and Its Limiting Factors ”, 1996 IEICE General Conference, SB-11-7, p747-748” is known.
[0003]
As shown in FIG. 17, the optical add / drop multiplexer ADM disclosed in this document includes two optical circulators OC provided in series in the optical fiber main line MF of the communication network.₁, OC₂And a transmission type optical fiber grating FG. The optical fiber grating FG includes a plurality of wavelength components λ.₁~ Λ_nSpecific wavelength component λ of signal light including_iOnly the reflected wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nIt has a demultiplexing characteristic that transmits light.
[0004]
Wavelength component λ₁~ Λ_nWhen the signal light containing is incident from the upstream side of the optical fiber main line MF, the optical circulator OC₁Port P₁To port P₂To the wavelength component λ by the optical fiber grating FG₁~ Λ_i-1, Λ_{i + 1}~ Λ_nThrough the optical circulator OC₂Port P_FourOr port P_FiveThrough the optical fiber main line MF. Further, the wavelength component λ is obtained by the optical fiber grating FG._iReflecting port P_ThreeBranch to (Drop).
[0005]
On the other hand, λ_iWavelength component λ of the same wavelength as_IOptical circulator OC₂Insertion port P₆This wavelength component λ_IPort P_FourTo the port P after being reflected by the optical fiber grating FG_FourOr port P_FiveThe wavelength component λ by propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nΛ_IIs output to the downstream side of the optical fiber main line MF.
[0006]
Thus, the conventional optical add / drop multiplexer ADM has two optical circulators OC.₁, OC₂In addition, by connecting the transmission type optical fiber grating FG in series in the optical fiber main line MF, branching (Drop) and insertion (Add) of arbitrary wavelength components are realized. JP-A-9-275374, JP-A-9-507313, JP-A-6-252890, WO97 / 34379, WO97 / 08574, JP11-11 Japanese Patent No. 511568, International Publication No. 97/28475, Japanese Patent Publication No. 11-503537, and Japanese Patent Application Laid-Open No. 6-160655 disclose techniques related to a conventional optical add / drop multiplexer.
[0007]
[Problems to be solved by the invention]
However, since the conventional optical add / drop multiplexer has a configuration in which a transmission type optical fiber grating FG is connected in series to the optical fiber main line MF, the demultiplexing characteristics for branching and inserting are changed or added. In this case, it is necessary to physically cut the optical fiber main line MF and install a separate optical add / drop device. Since the communication network must be disconnected in this way, it is not possible to easily change or add the demultiplexing characteristics, and in constructing a large-capacity wavelength division multiplexing optical communication network, expandability, etc. There was a big restriction on it. Furthermore, in order to change or add the demultiplexing characteristics, it is necessary to lay a large number of expensive and complicated optical circulators.
[0008]
The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an optical add / drop device having excellent expandability, simplicity, and low cost.
[0009]
[Means for Solving the Problems]
  The optical add / drop device of the present invention comprises:An optical add / drop device inserted in the middle of an optical transmission line that transmits signal light of a plurality of wavelengths,It is configured with a light reflector and a directional coupler, and as a light reflector,Transmits signal light of an arbitrarily selected wavelength among signal lights of multiple wavelengths and reflects signal light of other wavelengthsAs a directional coupler equipped with a light reflector,Connected to the upstream side in the middle of the optical transmission lineA first port;Connected downstream in the middle of the optical transmission lineOptically connected to the second port and the light reflectoringA third port,The signal light input to the first port is output from the third port to the light reflector, and the signal light input from the light reflector to the third port is output from the second port.And a directional coupler.
  The optical reflector is constituted by a fiber grating in which the period of the refractive index distribution gradually changes in a predetermined range along the longitudinal direction of the optical fiber. Alternatively, the optical reflector is configured by a fiber grating in which the average refractive index of the refractive index distribution gradually changes in a predetermined range along the longitudinal direction of the optical fiber. Alternatively, the optical reflector is configured by a fiber grating in which the average refractive index of the refractive index distribution changes stepwise in a predetermined range along the longitudinal direction of the optical fiber.
  Furthermore, the light reflector has a different reflection wavelength in each of the plurality of reflection regions included in the predetermined range, and changes the refractive index distribution in any one of the plurality of reflection regions to change the original reflection of the reflection region. It has the control mechanism which makes a wavelength a transmission wavelength.
[0010]
  The control mechanism is preferably a means for applying any one of heat, strain, and light to any one of the plurality of reflection regions, and more than one of heat, strain, and light. It is also preferable to have means for individually applying to each of the reflective areas.
[0014]
[Action]
In the optical add / drop multiplexer of the present invention, the optical transmission path is optically connected to the first port and the second port of the directional coupler, and the optical reflector is optically connected to the third port. Have Therefore, the optical reflector is not connected in series in the optical transmission line, but is connected to the optical transmission line via the directional coupler. According to this configuration, the signal light input to the first port from the upstream side of the optical transmission line is input to the optical reflector through the third port of the directional coupler, and the optical reflector receives the input signal light. Among them, the signal light of the selected wavelength is transmitted, the signal light of other wavelengths is reflected, and returned to the directional coupler through the third port. A directional coupler emits the reflected signal light from the second port to the downstream side of the optical transmission line.
[0015]
As described above, the optical add / drop multiplexer of the present invention can arbitrarily select the signal light wavelength in the optical transmission line without adopting a configuration in which the optical reflector is connected in series in the optical transmission line. Therefore, it is possible to branch or insert a desired signal light wavelength without disconnecting the optical transmission line, and to exhibit excellent expandability, simplicity, and low cost.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS. In these drawings, the same or corresponding components are denoted by the same reference numerals.
[0017]
(First embodiment)
An optical add / drop multiplexer according to a first embodiment will be described with reference to FIGS. In FIG. 1, the optical add / drop multiplexer ADM includes a plurality of wavelength components λ.₁~ Λ_nA directional coupler 2 that is optically connected to an optical transmission line (hereinafter referred to as an optical fiber main line) MF or the like for propagating signal light including a specific wavelength component λ_iAnd the remaining wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nA bidirectional optical reflector FG made of an optical fiber grating or the like having a demultiplexing characteristic for reflecting the light.
[0018]
First port (incident port) P of the directional coupler 2_inOptical connector C provided in_inAnd the second port (outgoing port) P_outOptical connector C provided in_outThe optical fiber main line MF etc. is connected to the third port (intermediate port) P_aOptical connector C provided in_aThe light reflector FG is connected to the port P at the other end of the light reflector FG._bOptical connector C provided in_bIn addition, a receiver, a transmitter, and the like are connected.
[0019]
Directional coupler 2 has port P_inSignal light incident on port P_aTo port P_aSignal light incident on port P_outHas a multi-stage port that propagates to For example, the directional coupler 2 sends signal light to the port P as shown in FIG._inTo P_a, P_outAn optical circulator 4 that guides nonreciprocally in this order, an optical fiber coupler 6 as shown in FIG. 3, and the like are used.
[0020]
In the optical add / drop multiplexer ADM having such a structure, wavelength components λ for a plurality of channels are provided.₁~ Λ_nThe signal light including the signal P is the port P of the directional coupler 2_inIs incident on port P_inTo port P_aTo the light reflector FG. Wavelength component λ by light reflector FG₁~ Λ_i-1, Λ_{i + 1}~ Λ_nIs reflected on port P_outAnd optical connector C_outTo the optical fiber main line MF. Further, the wavelength component λ is reflected by the light reflector FG._iThrough port P_bBranch to (Drop).
[0021]
On the other hand, λ_iWavelength component λ of the same wavelength as_IOptical connector C_bPort P through_bWhen this is inserted (Add), it is transmitted through the light reflector FG, and the port P_aThrough port P_outThe wavelength component λ by propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nΛ_IThe signal light including
[0022]
Thus, the optical add / drop multiplexer ADM includes a plurality of wavelength components λ.₁~ Λ_nIt is possible to branch or insert a desired wavelength component from the signal light including. Furthermore, optical connector C_a, C_bThe wavelength component to be branched or inserted can be easily changed or added simply by replacing the optical reflector FG provided detachably between them with an optical reflector having other demultiplexing characteristics. Particularly, since the optical reflector FG is not connected in series to the optical fiber main line MF or the like, the above wavelength components can be changed or added without physically cutting the optical fiber main line MF or the like. Therefore, it has extremely excellent expandability. Furthermore, since the configuration is simple, the manufacturing cost can be significantly reduced.
[0023]
The optical reflector FG is not limited to the optical fiber grating, but may be a grating formed in various optical waveguides, a dielectric multilayer optical filter, or the like.
[0024]
In addition, in order to guide the signal light between the directional coupler 2 and the light reflector FG, various optical waveguides such as an optical fiber and a planar optical waveguide can be used.
[0025]
In addition, a specific wavelength component λ_iInstead of the optical reflector FG having a demultiplexing characteristic that transmits the light, an optical reflector having a characteristic that reflects all the wavelength components of the signal light is provided, thereby providing an incident port P._inThe signal light incident on the output port P as it is_outCan be emitted.
[0026]
(Second Embodiment)
The optical add / drop device according to the second embodiment will be described with reference to FIGS. In FIG. 4, the difference from the first embodiment is described. A control mechanism CNT that variably controls the demultiplexing characteristics from the outside by applying heat, light, or mechanical stress to the light reflector FG. Is provided.
[0027]
An optical fiber grating is used for the light reflector FG. The optical fiber grating has a wavelength component λ in a static state where control by the control mechanism CNT is not performed.₁~ Λ_nAre reflected and controlled by the control mechanism CNT, the wavelength component λ₁~ Λ_nSpecific wavelength component λ of_iAnd the remaining wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nThe structure is such that the demultiplexing characteristics are changed so as to reflect the light.
[0028]
5 to 7 show an example of the structure of such an optical fiber grating and its demultiplexing characteristics.
[0029]
The optical fiber grating shown in FIG. 5A is a chirped grating having a structure in which the period of the refractive index distribution gradually changes along the longitudinal direction (axial direction of the optical waveguide) in the core of the optical fiber. As shown in FIG. (B), the wavelength component λ in the static state.₁~ Λ_nIt has a demultiplexing characteristic that reflects all of the above.
[0030]
The optical fiber grating shown in FIG. 6 (a) is a chirped grating having a structure in which the period of the refractive index distribution in the longitudinal direction is constant, but the refractive index gradually changes, as shown in FIG. 6 (b). In the static state, the wavelength component λ₁~ Λ_nIt has a demultiplexing characteristic that reflects all of the above.
[0031]
The optical fiber grating shown in FIG. 7 (a) is a chirped grating having a structure in which a plurality of gratings each having a refractive index distribution changed in a stepwise manner are arrayed in cascade, although the refractive index distribution period is constant. As shown in (b), in the static state, the wavelength component λ₁~ Λ_nIt has a demultiplexing characteristic that reflects all of the above.
[0032]
In FIG. 4, in the control mechanism CNT that thermally controls the light reflector FG, a plurality of heating elements such as a plurality of thermal heads and Peltier elements arranged along the longitudinal direction of the chirped grating are provided. A heat source unit 8 provided, and a drive unit 10 that supplies electric power to each heating element are provided. A control signal S for designating the electric energy of each heating element from the microcomputer system to the drive unit 10_DIs supplied, the chirped grating is partially expanded and contracted and the refractive index is changed by the heat generation (or cooling) of the designated heating element, and the refractive index distribution is partially changed. When the refractive index distribution is partially changed in this way, the wavelength component λ₁~ Λ_nThe chirped grating having the characteristic of totally reflecting the control signal S_DWavelength component λ specified by_iOnly transmits the remaining wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nIt changes to the demultiplexing characteristic that reflects.
[0033]
In the chirped grating shown in FIGS. 6 (a) and 6 (b), as shown in FIG. 6 (c), as shown in FIG. 6 (d), the heated portion and the refractive index of the portion are changed. It exhibits demultiplexing characteristics that transmit a specific wavelength.
[0034]
Moreover, in the chirped grating shown in FIGS. 7A and 7B, as shown in FIG. 7C, the chirped grating shown in FIG. As such, it exhibits a demultiplexing characteristic that transmits a specific wavelength.
[0035]
In the control mechanism CNT that applies mechanical stress to the light reflector FG, a piezo element or actuator that mechanically expands or contracts each part of the chirped grating is used instead of the heat source unit 8. Each part of the optical fiber grating is mechanically expanded and contracted by a piezo element and an actuator, and the refractive index of each part of the optical fiber grating is changed by this expansion and contraction so that a specific wavelength component is transmitted.
[0036]
The control mechanism CNT that irradiates light to the light reflector FG includes a light source that irradiates laser light or the like to each part of the chirped grating, and changes the refractive index of the part that is thermally expanded or contracted by the laser light. Thus, a specific sex wavelength component is transmitted.
[0037]
It is also possible to transmit a plurality of wavelength components by controlling a plurality of portions of the chirped grating with these control mechanisms CNT.
[0038]
Next, the operation of the optical add / drop multiplexer ADM having such a structure will be described. When control by the control mechanism CNT is not performed, a plurality of wavelength components λ₁~ Λ_nThe signal light including the signal P is the port P of the directional coupler 2_inIs incident on port P_aTo the light reflector FG, and the wavelength component λ is transmitted by the light reflector FG.₁~ Λ_nPort P reflecting all_aTo P_outTo exit.
[0039]
On the other hand, when the light reflector FG is controlled by the control mechanism CNT, the chirped grating is controlled by the control signal S._DWavelength component λ specified by_iProduces a demultiplexing characteristic. Thereby, the light reflector FG is connected to the port P of the directional coupler 2._aMore incident wavelength component λ₁~ Λ_nOf which the wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nReflecting port P_aTo P_outTo exit. Further, the wavelength component λ is reflected by the light reflector FG._iThrough port P_bBranch to (Drop).
[0040]
Further, in a state where the light reflector FG is controlled by the control mechanism CNT, λ_iWavelength component λ of the same wavelength as_IOptical connector C_bPort P through_bWhen this is inserted (Add), it is transmitted through the light reflector FG and transmitted through the port P._outThe wavelength component λ by propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nΛ_IThe signal light including
[0041]
As described above, the optical add / drop device ADM can variably control the demultiplexing characteristics of the light reflector FG by the control mechanism CNT. Therefore, the optical add / drop device ADM can be easily selected without requiring replacement of the light reflector FG. Can be branched or inserted. In particular, it is possible to change the demultiplexing characteristics of the light reflector FG simply by instructing the desired transmission wavelength to the control mechanism CNT, so that a communication network having functions such as a remote system and an automatic control system is constructed. It has excellent extensibility.
[0042]
(Third embodiment)
An optical add / drop device according to a third embodiment will be described with reference to FIGS.
[0043]
8, the optical add / drop device ADM includes an optical circulator 4 optically connected to the optical fiber main line MF and the like, and an optical reflector FG, as in the optical add / drop device of FIG. Furthermore, another directional coupler 12 is connected to the port P._cIs optically connected to the light reflector FG.
[0044]
The directional coupler 12 includes an insertion port P_dSignal light incident on port P_cPort P_cSignal light incident on port P_eTo each port P_d, P_eIncludes an optical connector C for connecting a receiver, transmitter, etc._d, C_eIs provided.
[0045]
The directional coupler 12 is provided with an insertion port P as shown in FIG._dThe signal light incident on_c, P_eAn optical circulator 14 that guides nonreciprocally in this order, an optical fiber coupler 16 as shown in FIG. 10, and the like are used.
[0046]
In the optical add / drop multiplexer ADM having such a structure, a plurality of wavelength components λ₁~ Λ_nThe signal light including_inIs incident on port P_aTo the light reflector FG. In the optical reflector FG having a demultiplexing characteristic that transmits a specific wavelength component, the wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nIs reflected on port P_aThrough port P_outTo exit. Further, in the light reflector FG, the wavelength component λ_iAnd propagates to the directional coupler 12 and passes through the branch port P_eDrop to.
[0047]
Also, λ_iWavelength component λ of the same wavelength as_IOptical connector C_dPort P for insertion_dWhen the directional coupler 12 is inserted into the port P,_cTo the light reflector FG, and this wavelength component λ is transmitted by the light reflector FG._ITransparent. Further, the optical circulator 4 is connected to the port P._aThrough port P_outThe wavelength component λ by propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nΛ_IThe signal light including
[0048]
As described above, according to this embodiment, the branch port P for branching the desired wavelength component with a simple structure._dAnd an insertion port P for inserting a desired wavelength component_eIt is possible to provide an optical add / drop device comprising: Connector C_a, C_bA desired wavelength component can be branched or inserted simply by replacing the optical reflector FG that is detachably connected between them with an optical reflector having other demultiplexing characteristics. Further, the control mechanism CNT and the light reflector FG shown in FIG. 4 can be applied.
[0049]
FIG. 11 shows a modification of the optical add / drop multiplexer realizing a simpler structure. This optical add / drop device ADM includes an optical fiber coupler 18 and its port P_aAnd branch port P_eA light reflector FG such as an optical fiber grating is optically connected between them. In addition, port P_dIs the insertion port, port P_inAnd P_outTo the optical fiber main line FL of the communication network.
[0050]
The optical add / drop multiplexer ADM having such a structure has the port P_inMultiple wavelength components λ incident on₁~ Λ_nIs propagated to the optical reflector FG through the coupling portion of the optical fiber coupler 18, and a specific wavelength component λ is transmitted by the optical reflector FG._iPort P for branching through_eBranch to (Drop). Further, the remaining wavelength component λ is reflected by the light reflector FG.₁~ Λ_i-1, Λ_{i + 1}~ Λ_n, And the port P again through the optical coupler 18_outTo exit.
[0051]
On the other hand, λ_iWavelength component λ of the same wavelength as_IOptical connector C_dPort P for insertion_dIs inserted into the port P through the optical fiber coupler 18._outThe wavelength component λ by propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nΛ_IThe signal light including
[0052]
Thus, according to this modification, it is possible to provide an optical add / drop device capable of branching or inserting a desired wavelength component with an extremely simple structure.
[0053]
FIG. 12 shows still another modification. The optical add / drop device ADM includes an optical fiber coupler 20 and an intermediate port P thereof._aAnd branch port P_eAn optical reflector FG such as an optical fiber grating is optically connected between the other intermediate port P_a'And insertion port P_dA light reflector FG 'having the same demultiplexing characteristics as the light reflector FG is optically connected therebetween. Furthermore, the optical path length L from the optical coupling portion of the optical fiber coupler 20 to the optical reflector FG₁And the optical path length L from the optical coupling portion of the optical fiber coupler 20 to the optical reflector FG '.₂Ratio L₁/ L₂Is set to an integer multiple.
[0054]
The optical add / drop multiplexer ADM having such a structure has a plurality of wavelength components λ.₁~ Λ_nSignal light including_inIs transmitted to the optical reflectors FG and FG ′ through the optical fiber coupler 20.
[0055]
Here, the optical fiber coupler 20 has a port P located on the diagonal side._in, P_aBetween each other or port P_out, P_bThe phase of the light propagating between the two is changed by π / 2, and the port P not located on the diagonal side_in, P_bBetween each other or port P_out, P_aIt has a characteristic that the phase of light propagating between the two is not changed. Therefore, the wavelength component λ propagating to the light reflector FG₁~ Λ_nThe phase of the wavelength component λ changes by π / 2 and propagates to the optical reflector FG ′.₁~ Λ_nThe phase of does not change.
[0056]
The light reflector FG transmits the wavelength component λ propagating from the optical fiber coupler 20 in this way.₁~ Λ_nOf which the wavelength component λ_iPort P for branching through_eBranch to (Drop). Furthermore, the wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nAnd the port P again through the optical fiber coupler 20_outTo exit. Similarly, the optical reflector FG ′ also transmits the wavelength component λ propagating from the optical fiber coupler 20._iThe wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nAnd the port P again through the optical fiber coupler 20_outTo exit.
[0057]
However, the port P is reflected by the light reflector FG._outWavelength component λ propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_n, Has already changed by π / 2 as described above, but does not change further when passing through the optical fiber coupler 20 again. On the other hand, the port P is reflected by the light reflector FG._inWavelength component propagating to the side λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nHas already changed by π / 2 as described above, and further changes by π / 2 when passing through the optical fiber coupler 20, resulting in a total phase change of π. In addition, the light is reflected by the light reflector FG 'and port P_outWavelength component λ propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nIs changed by π / 2 for the first time when passing through the optical fiber coupler 20 again. On the other hand, the light is reflected by the light reflector FG 'and port P_inWavelength component propagating to the side λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nThe phase of does not change. Furthermore, the optical path length L₁And L₂Ratio L₁/ L₂Is set to an integer multiple.
[0058]
Therefore, the light is reflected by the light reflectors FG and FG 'and is transmitted to the port P_inTwo wavelength components λ propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nAre out of phase with each other, cancel each other and disappear._inI will not return. In addition, the light is reflected by the light reflectors FG and FG 'and the port P_outTwo wavelength components λ propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nSince they have the same phase, they are combined and emitted.
[0059]
Thus, port P_outFrom the wavelength component λ with less attenuation of light intensity₁~ Λ_i-1, Λ_{i + 1}~ Λ_nCan be emitted.
[0060]
λ_iWavelength component λ of the same wavelength as_IOptical connector C_dPort P for insertion_dIs inserted into (Add), the light is transmitted through the optical reflector FG ', and is transmitted through the optical fiber coupler 20 to the port P._outPropagate to. Therefore, the wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nΛ_IPort P_outTo exit.
[0061]
As described above, according to the optical add / drop multiplexer ADM, it is possible to branch and insert a desired wavelength component with an extremely simple structure. In particular, port P_inPort P without attenuating signal light incident on_outTherefore, it exhibits excellent effects in use such as construction of a high-quality optical communication network.
[0062]
(Fourth embodiment)
An optical add / drop multiplexer according to a fourth embodiment will be described with reference to FIG.
[0063]
This optical add / drop device ADM has an intermediate port P between two optical fiber couplers 22 and 24._a, P_bAnd intermediate port P_a', P_bThe light reflectors FG and FG 'are optically connected to each other. These optical reflectors FG and FG ′ are both optical fiber gratings having the same demultiplexing characteristics, and have a plurality of wavelength components λ.₁~ Λ_nWhen signal light containing is incident, a specific wavelength component λ_iAnd the remaining wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nHas a demultiplexing characteristic.
[0064]
Furthermore, the optical path length L from the optical coupling portion of the optical fiber coupler 22 to the optical reflector FG₁₁And the optical path length L from the optical coupling portion of the optical coupler 22 to the optical reflector FG '.₁₂Ratio L₁₁/ L₁₂Is set to an integer multiple. Similarly, the optical path length L from the optical coupling portion of the optical fiber coupler 24 to the optical reflector FG_{twenty one}And an optical path length L from the optical coupling portion of the optical coupler 16 to the optical reflector FG '._{twenty two}Ratio L_{twenty one}/ L_{twenty two}Is also set to an integer multiple.
[0065]
Next, the operation of the optical add / drop multiplexer ADM having such a structure will be described. Multiple wavelength components λ₁~ Λ_nIs included in the optical fiber coupler 22 port P._in, The signal light whose phase is changed by π / 2 in the optical fiber coupler 22 propagates to the optical reflector FG, and the signal light having no phase change propagates to the optical reflector FG ′.
[0066]
Both of the light reflectors FG and FG ′ have a wavelength component λ._iIs transmitted to the optical fiber coupler 24, and the remaining wavelength component λ is transmitted.₁~ Λ_i-1, Λ_{i + 1}~ Λ_nIs reflected to the optical fiber coupler 22 side. The optical fiber coupler 22 transmits these reflected wavelength components λ.₁~ Λ_i-1, Λ_{i + 1}~ Λ_nPort P_outTo exit.
[0067]
Here, the optical path length L₁₁And L₁₂Ratio L₁₁/ L₁₂Is set to an integral multiple, and the optical fiber coupler 22 is connected to the port P located on the diagonal side._in, P_aBetween each other or port P_out, P_bThe phase of the light propagating between the two is changed by π / 2, and the port P not located on the diagonal side_in, P_bBetween each other or port P_out, P_aIt has a characteristic that the phase of light propagating between the two is not changed.
[0068]
For this reason, it is reflected by the optical reflectors FG and FG 'and is port P of the optical fiber coupler 22._inTwo wavelength components λ propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nAre out of phase with each other, cancel each other and disappear._inI will not return. Further, it is reflected by the optical reflectors FG and FG 'and is port P of the optical fiber coupler 22._outTwo wavelength components λ propagating to₁~ Λ_i-1, Λ_{i + 1}~ Λ_nSince they are in phase with each other, they are combined and emitted. Thus, port P_outFrom λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nCan be emitted.
[0069]
Wavelength component λ transmitted through the light reflectors FG and FG ′_iThrough the optical fiber coupler 24_d, P_ePropagate to.
[0070]
However, as with the optical fiber coupler 22, the optical fiber coupler 24 also has a port P located on the diagonal side._b, P_dBetween each other or port P_b', P_eThe phase of the light propagating between the two is changed by π / 2, and the port P not located on the diagonal side_b, P_eBetween each other or port P_b', P_dIt has a characteristic that the phase of light propagating between the two is not changed. Furthermore, the optical path length L_{twenty one}And L_{twenty two}Ratio L_{twenty one}/ L_{twenty two}Is set to an integer multiple.
[0071]
Therefore, the insertion port P from the light reflector FG_dWavelength component λ propagating to_iAnd the insertion port P from the light reflector FG '_dWavelength component λ propagating to_iIs out of phase, cancels and disappears, so the insertion port P is substantially_dIs not emitted.
[0072]
On the other hand, the port P for branching from the light reflector FG ′_eWavelength component λ propagating to_iAnd a port P for dropping from the optical reflector FG '_eWavelength component λ propagating to_iAre in phase. Therefore, these wavelength components λ_iAre combined with each other to form a branching port P_eBranch to (Drop).
[0073]
Next, λ_iWavelength component λ of the same wavelength as_IOptical connector C_dPort P for insertion_dIs transmitted to the optical reflectors FG and FG 'through the optical fiber coupler 24, and further transmitted through the optical reflectors FG and FG' via the optical fiber coupler 22 to the port P._outPropagate to.
[0074]
Here, the characteristics of the optical fiber couplers 22 and 24 described above and the optical path length L₁₁, L₁₂, L_{twenty one}, L_{twenty two}Therefore, the port P of the optical fiber coupler 22 is transmitted through the optical reflectors FG and FG '._inWavelength component propagating to the side λ_ICancels out of phase and is essentially port P_inDoes not propagate to Further, the light passes through the optical reflectors FG and FG ′ and passes through the port P of the optical fiber coupler 22._outWavelength component λ propagating to_IAre combined in the same phase. Therefore, the insertion port P_dDesired wavelength component λ_IIs inserted (Add), the port P of the optical fiber coupler 22 is added._outThe wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nΛ_IAnd output as signal light including
[0075]
Thus, according to this embodiment, the port P_inPort P without returning the signal light incident on_outAnd the inserted wavelength component is also transmitted to port P._inPort P without propagating to_outSince the light is emitted to the light source, interference and the like can be greatly suppressed.
[0076]
The optical reflectors FG and FG ′ are optical reflectors that transmit a plurality of wavelength components and reflect the remaining wavelength components, whereby a plurality of wavelength components can be branched and inserted.
[0077]
Further, by making the light reflectors FG and FG 'detachable, the wavelength component to be branched or inserted can be easily changed. Further, the chirp grating described in the second embodiment may be used for the light reflectors FG and FG ′, and the demultiplexing characteristics may be variably controlled by the control mechanism CNT.
[0078]
Further, by applying a total reflection type light reflector, the incident port P_inThe signal light incident on the output port P as it is_outCan be emitted.
[0079]
(Fifth embodiment)
An optical add / drop multiplexer according to a fifth embodiment will be described with reference to FIG.
[0080]
In this optical add / drop multiplexer ADM, a part of a pair of single mode optical fibers is fused, and a grating is integrally formed in an optical coupling portion formed by the fusion, thereby integrating the optical reflector FG. An optical coupler 26 is provided. A grating has a plurality of wavelength components λ₁~ Λ_nA specific wavelength component λ_iAnd the remaining wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nDemultiplexing characteristics are reflected.
[0081]
The optical add / drop multiplexer ADM having such a structure has the port P_inMultiple wavelength components λ₁~ Λ_nWhen the signal light is incident, the wavelength component λ is reflected by the light reflector FG._iPort P for branching through_eDrop to the remaining wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nReflecting port P_outTo exit.
[0082]
Also, the insertion port P_dAnd λ_iWavelength component λ of the same wavelength as_IIs transmitted through the light reflector FG, and the wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nWavelength component λ_IThe signal light including the port P_outTo exit.
[0083]
Thus, according to this embodiment, it is possible to provide a low-cost optical add / drop device with an extremely simple structure.
[0084]
Further, by integrally forming a total reflection type grating in the optical coupling portion, the incident port P_inThe signal light incident on the output port P as it is_outCan be emitted.
[0085]
(Sixth embodiment)
An optical add / drop multiplexer according to a sixth embodiment will be described with reference to FIGS. 15 and 16.
[0086]
In FIG. 15, this optical add / drop multiplexer ADM includes a port P of an optical circulator 28 that is a directional coupler._aAnd a plurality of optical connectors C₁~ C_nA light reflector FG comprising a plurality of optical fiber gratings₁~ FG_nAre connected in series. Each light reflector FG₁~ FG_nThe optical connector C₁~ C_nIs detachably connected.
[0087]
Each light reflector FG₁~ FG_nAs the light reflector on the optical circulator 28 side (front stage side) transmits the wavelength components for many channels and goes to the light reflector on the rear stage side, the light reflector on the front stage side is different. It is set so as to transmit a part of the wavelength components transmitted in (1). Furthermore, each light reflector FG₁~ FG_nAre set to reflect wavelength components other than the transmission wavelength band set as described above.
[0088]
More specifically, the front stage light reflector FG₁Is a plurality of wavelength components λ₁~ Λ_nWavelength component λ of signal light including₁~ Λ_iAnd the remaining wavelength component λ_{i + 1}~ Λ_nThe second stage optical reflector FG₂Is the wavelength component λ₁~ Λ_iSpecific wavelength component λ of₁~ Λ_i-1Etc., and the remaining wavelength component λ_iIs set to a demultiplexing characteristic that reflects the light. Third stage light reflector FG_ThreeIs the wavelength component λ₁~_i-1Specific wavelength component λ of₁~ Λ_i-2Etc., and the remaining wavelength component λ_i-1Is set to a demultiplexing characteristic for reflecting the light. Similarly, the rear-stage light reflector is set to a demultiplexing characteristic having a transmission wavelength band narrower than the transmission wavelength band of the front-stage light reflector.
[0089]
Next, the operation of this optical add / drop multiplexer ADM will be described. In FIG. 15, the last-stage light reflector FG_nIs a total reflection type, and a light reflector FG provided in the preceding stage_n-1Is the wavelength component λ₁And have a demultiplexing characteristic of reflecting other wavelength components.
[0090]
Multiple wavelength components λ₁~ Λ_nSignal light including_inIs incident on the port P of the optical circulator 28_aLight reflector FG through₁~ FG_nPropagate to the side. Light reflector FG₁~ FG_nReflects and transmits the wavelength component incident from the preceding stage according to the respective demultiplexing characteristics. For this reason, the front stage light reflector FG₁Is the wavelength component λ_{i + 1}~ Λ_nIs reflected to the optical circulator 28 side, and once transmitted, the optical reflector FG₂~ FG_nWavelength component λ reflected back from₁~ Λ_iIs transmitted again to the optical circulator 28 side.
[0091]
Therefore, when the desired wavelength component is not dropped or added (added), the port P_inThe signal light incident on the port P_outCan be propagated to.
[0092]
Last stage light reflector FG_nOptical connector C_nWhen removed from the optical connector C_nFrom the wavelength component λ₁Can be dropped. Furthermore, the light reflector FG_nWith λ removed₁Wavelength component λ of the same wavelength as₁'Optical connector C_nThis wavelength component λ₁'Is the front light reflector FG_n-1~ FG₁Through the port P of the optical circulator 28_outPropagate to.
[0093]
Moreover, the light reflector FG located in the intermediate stage_ThreeEtc., the optical connector C_ThreeTo wavelength component λ₁~ Λ_i-1Can be dropped. Furthermore, the light reflector FG_ThreeWith λ removed₁~ Λ_i-1A wavelength component (one or a plurality of wavelength components) having the same wavelength as any of the optical connector C_ThreeWhen inserted into (Add), the inserted wavelength component becomes the light reflector FG.₁Or port P through optical circulator 28_outPropagate to.
[0094]
As described above, the optical add / drop multiplexer ADM includes the port P of the optical circulator 28._inIn addition, the optical reflector FG satisfying the above condition of the demultiplexing characteristic₁~ FG_nAs a result, the desired wavelength component can be dropped or inserted (Add).
[0095]
In addition, as long as the condition of the demultiplexing characteristic is satisfied, the light reflector FG₁~ FG_nSince the number of connections can be arbitrarily set, an optical add / drop multiplexer with a very high degree of freedom can be provided.
[0096]
Although the case where the optical circulator 28 is used has been described, the optical fiber coupler 6 shown in FIG. 3 may be used instead. Also, the light reflector FG₁~ FG_nIn addition to the optical fiber grating, an optical filter such as a dielectric multilayer film filter can be used. Further, the optical waveguide for guiding the signal light is not limited to the optical fiber.
[0097]
Next, a modification of the present embodiment will be described with reference to FIG. The optical add / drop multiplexer shown in FIG. 15 has one specific port P of the optical circulator 28 that separates signal light nonreciprocally._aLight reflector FG₁~ FG_nWere connected in series.
[0098]
On the other hand, the optical add / drop multiplexer ADM shown in FIG. 16 employs an optical circulator 30 having a larger number of ports and connects one or more optical reflectors to each port. Note that the optical circulator 30 shown in FIG._in, P_out, P_a1, P_a2, P_a3Port P_inSignal light incident on port P_a1, P_a2, P_a3, P_outThe structure propagates nonreciprocally in this order.
[0099]
Each port P_a1, P_a2, P_a3Reflector FG connected to₁₁~ FG_1n, FG_{twenty one}~ FG_2n, FG₃₁~ FG_3nIs a plurality of light reflectors FG shown in FIG. 15 for each port.₁~ FG_nSatisfies the conditions of the same demultiplexing characteristics.
[0100]
That is, the light reflector on the optical circulator 30 side (front stage side) transmits the wavelength components for many channels, and the closer to the rear stage light reflector, the more the wavelength component transmitted by the front stage light reflector. Are set so as to transmit some wavelength components.
[0101]
More specifically, port P_a1Reflector FG connected to₁₁Is the wavelength component λ_iAnd the remaining wavelength component λ₁~ Λ_i-1, Λ_{i + 1}~ Λ_nReflect. Light reflector FG_1nIs the wavelength component λ_iReflect. Port P_a2Reflector FG connected to_{twenty one}Is the wavelength component λ_jAnd the remaining wavelength component λ₁~ Λ_j-1, Λ_{j + 1}~ Λ_nReflect. Light reflector FG_2nIs at least the wavelength component λ_jReflect. Port P_a3Reflector FG connected to₃₁Is the wavelength component λ_kAnd the remaining wavelength component λ₁~ Λ_k-1, Λ_{k + 1}~ Λ_nReflect. Light reflector FG_3nIs at least the wavelength component λ_kReflect. Also, each light reflector FG₁₁~ FG_1n, FG_{twenty one}~ FG_2n, FG₃₁~ FG_3nAn optical fiber grating is used and is detachably connected by an optical connector.
[0102]
Next, the operation of the optical add / drop multiplexer ADM having such a configuration will be described. Multiple wavelength components λ₁~ Λ_nSignal light including_inIs incident on the light reflector FG₁₁~ FG_1n, FG_{twenty one}~ FG_2n, FG₃₁~ FG_3nWavelength component λ₁~ Λ_nTotal reflection of port P_outTo exit.
[0103]
Light reflector FG₁₁Is removed from the optical connector, the wavelength component λ_iDrops. In addition, λ_iWavelength component λ of the same wavelength as_iWhen 'Add' is inserted, the light reflector FG₁₁Through the port P of the optical circulator 30_outTo exit.
[0104]
Also, the light reflector FG_2nAnd FG_3nAre removed from the optical connectors, the wavelength component λ_jAnd λ_kDrops. In addition, λ_jOr λ_kWavelength component λ of the same wavelength as_j'Or λ_kWhen 'is inserted (Add), these wavelength components λ_j'Or λ_k'Is a light reflector FG_{twenty one}And FG₃₁Through the port P of the optical circulator 30_outPropagate to.
[0105]
As described above, the optical add / drop multiplexer ADM includes a plurality of ports P of the optical circulator 30._a1, P_a2, P_a3In addition, it has an extremely excellent effect that a desired wavelength component can be dropped (added) or inserted (added) by appropriately attaching and detaching a light reflector that satisfies a predetermined demultiplexing characteristic condition. ing. In particular, it is possible to provide an optical add / drop device with a very high degree of freedom and excellent extensibility.
[0106]
Incidentally, the respective light reflectors shown in FIG. 15 or FIG. 16 may be provided with the control mechanism CNT shown in FIG. 4 to control the respective demultiplexing characteristics.
[0107]
【The invention's effect】
As described above, according to the present invention, the optical transmission line connected to the first port and the second port of the directional coupler can be disconnected only by adjusting the demultiplexing characteristic of the optical reflector. In addition, wavelength components for branching or insertion can be arbitrarily set. Therefore, it is possible to provide an optical add / drop device that is excellent in operational simplicity and excellent in flexibility and expandability. Furthermore, since it can be realized with a small number of components, an optical add / drop multiplexer having low cost can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an optical add / drop multiplexer according to a first embodiment.
FIG. 2 is an explanatory diagram showing a specific example of a directional coupler.
FIG. 3 is an explanatory diagram showing another specific example of the directional coupler.
FIG. 4 is a block diagram illustrating a configuration of an optical add / drop multiplexer according to a second embodiment;
FIG. 5 is an explanatory diagram showing a normalized refractive index distribution and demultiplexing characteristics of a chirped grating.
FIG. 6 is an explanatory diagram showing a normalized refractive index distribution and demultiplexing characteristics of another chirped grating.
FIG. 7 is an explanatory diagram showing a normalized refractive index distribution and demultiplexing characteristics of still another chirped grating.
FIG. 8 is a block diagram illustrating a configuration of an optical add / drop multiplexer according to a third embodiment.
FIG. 9 is a block diagram showing a configuration of a modification of the optical add / drop multiplexer.
FIG. 10 is a block diagram showing a configuration of another modification of the optical add / drop multiplexer.
FIG. 11 is a block diagram showing a configuration of still another modification of the optical add / drop multiplexer.
FIG. 12 is a block diagram showing a configuration of still another modification of the optical add / drop multiplexer.
FIG. 13 is a block diagram illustrating a configuration of an optical add / drop multiplexer according to a fourth embodiment.
FIG. 14 is a block diagram illustrating a configuration of an optical add / drop multiplexer according to a fifth embodiment.
FIG. 15 is a block diagram illustrating a configuration of an optical add / drop multiplexer according to a sixth embodiment.
FIG. 16 is a block diagram showing a configuration of a modified example of the optical add / drop multiplexer of the sixth embodiment.
FIG. 17 is a block diagram showing a configuration of a conventional optical add / drop multiplexer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 2,12 ... Directional coupler, 4, 14, 28, 30 ... Optical circulator, 6, 16, 18, 20, 22, 24, 26 ... Optical fiber coupler, 8 ... Heat source part, 10 ... Drive part, ADM ... Optical add / drop multiplexer, FG, FG ', FG₁~ FG_n, FG₁₁~ FG_1n, FG_{twenty one}~ FG_2n, FG₃₁~ FG_3n... Light reflector, P_in, P_out, P_a, P_b, P_c, P_d, P_e, P_a1, P_a2, P_a3…port.

Claims (5)

An optical add / drop device inserted in the middle of an optical transmission line that transmits signal light of a plurality of wavelengths,
A light reflector that transmits signal light of an arbitrarily selected wavelength among the signal lights of the plurality of wavelengths and reflects signal light of other wavelengths ;
A first port connected to the upstream side in the middle of the optical transmission line, a second port connected to the downstream side in the middle of the optical transmission line is optically coupled to the optical reflector A signal that is input to the first port from the third port to the optical reflector, and that is input from the optical reflector to the third port. A directional coupler for outputting light from the second port ;
Comprising
The optical reflector is constituted by a fiber grating in which the period of the refractive index distribution gradually changes in a predetermined range along the longitudinal direction of the optical fiber, and the reflection wavelength in each of the plurality of reflection regions included in the predetermined range is different and have a control mechanism for a transmission wavelength of the original reflection wavelength of the reflection area by changing the refractive index distribution in the one of the reflective areas of said plurality of reflective areas,
An optical add / drop device . An optical add / drop device inserted in the middle of an optical transmission line that transmits signal light of a plurality of wavelengths,
A light reflector that transmits signal light of an arbitrarily selected wavelength among the signal lights of the plurality of wavelengths and reflects signal light of other wavelengths ;
A first port connected to the upstream side in the middle of the optical transmission line, a second port connected to the downstream side in the middle of the optical transmission line is optically coupled to the optical reflector A signal that is input to the first port from the third port to the optical reflector, and that is input from the optical reflector to the third port. A directional coupler for outputting light from the second port ;
Comprising
The optical reflector is configured by a fiber grating in which an average refractive index of a refractive index distribution gradually changes in a predetermined range along the longitudinal direction of the optical fiber, and is reflected in each of a plurality of reflection regions included in the predetermined range. Having a control mechanism in which the wavelength is different and the refractive index distribution in any one of the plurality of reflection regions is changed so that the original reflection wavelength of the reflection region is the transmission wavelength
An optical add / drop device . An optical add / drop device inserted in the middle of an optical transmission line that transmits signal light of a plurality of wavelengths,
A light reflector that transmits signal light of an arbitrarily selected wavelength among the signal lights of the plurality of wavelengths and reflects signal light of other wavelengths ;
A first port connected to the upstream side in the middle of the optical transmission line, a second port connected to the downstream side in the middle of the optical transmission line is optically coupled to the optical reflector A signal that is input to the first port from the third port to the optical reflector, and that is input from the optical reflector to the third port. A directional coupler for outputting light from the second port ;
Comprising
The optical reflector is configured by a fiber grating in which an average refractive index of a refractive index distribution changes stepwise in a predetermined range along the longitudinal direction of the optical fiber, and in each of a plurality of reflection regions included in the predetermined range. The reflection wavelength is different , and has a control mechanism that changes the refractive index distribution in any one of the plurality of reflection regions so that the original reflection wavelength of the reflection region is a transmission wavelength.
An optical add / drop device . The said control mechanism is a means to provide any one of a heat | fever, a distortion | strain, and light with respect to any reflective area | region among these reflective areas, The any one of Claims 1-3 characterized by the above-mentioned. The optical add / drop device described. 5. The optical add / drop device according to claim 4 , wherein the control mechanism includes means for individually applying any one of heat, strain, and light to each of the plurality of reflection regions .

Images