CN2341161Y - High isolation optical fiber grating style divider - Google Patents

Abstract

The utility model belongs to the technical field of structure design for wavelength division multiplexers, which comprises two circulators; a first optical grating is connected by using optical fibers; two circulator is connected with a second optical grating, and an isolator between the first optical grating and the second optical grating can be connected via the optical fiber. Under the condition without improving the peak value of the optical grating, the utility model can lower guided power with coherent interference to the close level with noncoherent interference. The coherent interference between upper signals and lower signals can be effectively reduced.

Description

High-isolation grating type optical fiber optical add/drop multiplexer

The utility model belongs to the structure-design technique field of wavelength division multiplexer, particularly grating type optical fiber light insert multiplexer architecture advances design.

The development of information highway has proposed the requirement of long distance, high capacity, two-forty to communication.Wavelength-division multiplex (WDM) is the desirable implementation of this requirement.(Optical Add/Drop Multiplexer OADM) is one of the Primary Component of wavelength-division multiplex system to optical add/drop multiplexer.Common add-drop multiplexer or demodulation multiplexer comprise the blazed grating color dispersion-type, interference filter type (as the F-P wave filter), the multi-coated interference type, planar lightwave circuit (PLC) type (array waveguide grating AWG), and active power filtering type (as electric light, acousto-optic filter, DFB-LD tunable optic filter) or the like.Fiber bragg grating device has that volume is little, inherent loss is low, frequency spectrum can be selected, easily with advantage such as fibre system coupling, be a kind of desirable selection of optical add-drop multiplexer.

The basic structure of the belt type optical add/drop multiplexer of fiber grating is made up of 11,12 and fiber gratings 13 of two circulators as shown in Figure 1, and the wavelength of incident is λ ₁, λ ₂, λ _i... the light of the n of a λ n passage is entered by the port one of first circulator 11, after this circulator port 2, incides fiber grating 13, and wavelength is λ _iLight be reflected, solve from this circulator port 3, and remaining light continues to propagate road situation down that Here it is.When setting out on a journey situation, the signal that set out on a journey enters from second circulator 12 port one, after this circulator port 2, is reflected by fiber grating 13, goes out from this circulator port 3.

In this add-drop multiplexer, there be two types crosstalk.First kind, coherent crosstalk, promptly set out on a journey and following road signal between crosstalk, this is because the peak reflectivity of grating can not equal 100%, always some go up (descend) road signal through under the grating pair (on) signal generation in road crosstalks.Second kind, incoherent crosstalking, promptly adjacent channel is to crosstalking that following road signal produces, the side mode suppression ratio of grating is high more, this crosstalk just more little.The ratio of power and the signal power of crosstalking is x.For coherent crosstalk, the electric field of superposed signal can be written as: $E\left(t\right)=E{d}_s\left(t\right)\cos [{\mathrm{\ω}}_{0}t+{\mathrm{\φ}}_s(t\left)\right]+\sqrt{x}E{d}_x\left(t\right)d_s\left(t\right)\cos [{\mathrm{\ω}}_{0}t+{\mathrm{\φ}}_x(t\left)\right]-----\left(1\right)$ Wherein, d _s(t), d _x(t) be two-valued function 0 or 1 at random, representation signal and the bit stream of crosstalking.When x＜＜1, detected power is: $P\left(t\right)=\frac{1}{2}{E}^2\left[d_s\right(t)+2{\sqrt{x}d}_s(t\left)d_x\right(t\left)\cos \right({\mathrm{\φ}}_s\left(t\right)+{\mathrm{\φ}}_x\left(t\right)\left)\right]---\left(2\right)$ To signal 0, P (t)=0.To signal 1, $P\left(t\right)\∈\left[\frac{1}{2}{E}^2\right(1-2\sqrt{x}),\frac{1}{2}{E}^2(1+2\sqrt{x}\left)\right]$ Obtaining Power penalty thus is: $p=-101g(1-4\sqrt{x})=-101g(1-4\sqrt{\frac{1-R}{R}})---\left(3\right)$ Wherein R is the peak reflectivity of grating.Crosstalk for incoherent, signal cross-talk power is the simple superposition relation, and Power penalty is:

P=-10lg (1-2x) (4) wherein x is the side mode suppression ratio of two adjacent channels.For at a distance of farther channel, crosstalk and generally can ignore.

Fig. 2 is under coherent crosstalk and the incoherent two kinds of situations of crosstalking, Power penalty and the relation of crosstalking.Solid line is crosstalking of path channels up and down among the figure, and dotted line is crosstalking of adjacent channel, as can be seen, crosstalks when identical, and the Power penalty that coherent crosstalk is introduced is crosstalked much larger than incoherent.Therefore, in above-mentioned basic structure, for improving the performance of device, the peak reflectivity that improves grating is primary, and next is only manages to improve side mode suppression ratio.Calculating shows that the Power penalty that will make coherent crosstalk is less than 1dB, and the peak reflectivity of grating must be greater than 99.7%, and this has proposed high requirement for the making of grating.Even accomplished so high reflectivity during experiment, also had degenerate problem.During actual the use, also can cause system performance degradation owing to cloth loudspeaker lattice wave personal attendant's temperature drift of grating or channel wavelength drift make channel depart from reflection peak.This is the weak point of above-mentioned optical add-drop multiplexer.

The purpose of this utility model is, for overcoming the weak point of prior art, proposes a kind of cascaded fiber grating type optical add-drop multiplexer, makes it can effectively reduce coherent crosstalk between the signal of road up and down.

The utility model is designed a kind of cascaded fiber grating type optical add-drop multiplexer, be included between two circulators and connect first grating with optical fiber, it is characterized in that, in said two circulators, also be connected with second grating, between said first, second grating, also connect an isolator with optical fiber.Its structure as shown in Figure 3.

Principle of work of the present utility model is: the wavelength of incident is λ ₁, λ ₂, λ _i... the light of the several passages of λ n is entered by the port one of first circulator 21, after this circulator port 2, incides first fiber grating 22, and wavelength is λ ₁Light be reflected, solve from this circulator port 3, and remaining light continues to propagate road situation down that Here it is.When setting out on a journey situation, the signal that set out on a journey enters from second circulator 24 port one, after this circulator port 2, by 25 reflections of second fiber grating, goes out from port 3.The signal of setting out on a journey is reflected with different gratings with following road signal, the middle isolator 23 that adds, this just can reduce the coherent crosstalk between the signal of road up and down effectively.For example, have two cloth loudspeaker lattice wave appearance together, peak reflectivity is 95% fiber grating (this grating can't use in basic structure shown in Figure 1 at all).When multi-wavelength signals after the port one incident of first circulator, the long wide part of cloth loudspeaker lattice wave is reflected, but still have 5% light can see through first grating, through behind the isolator, run into second grating, finally have only 0.25% power can see through second grating, the signal of setting out on a journey is produced crosstalk.And for setting out on a journey signal, because the effect of isolator can not produce following road signal in theory and crosstalk.Like this, the coherent crosstalk in this device just has been greatly diminished.Following road signal can be written as the Power penalty that the coherent crosstalk of the signal of setting out on a journey brings: $p=-101g(1-4\sqrt{\frac{{(1-R)}^2}{R}})------------\left(5\right)$ Wherein, R is the peak reflectivity of grating.

When Fig. 4 is to use the identical grating of transmissivity, the contrast of the Power penalty that coherent crosstalk is introduced in this cascaded fiber grating new construction of the utility model and the above-mentioned basic structure.Solid line is the situation of above-mentioned basic structure among the figure, and dotted line is the situation of new structure.With Fig. 2 more as can be seen, adopt this new construction, the Power penalty that coherent crosstalk can be introduced under the situation that need not improve the grating peak value is reduced to and the incoherent approaching level of crosstalking.

Brief Description Of Drawings:

Fig. 1 is the basic structure synoptic diagram of prior art.

Fig. 2 is under the coherent crosstalk and the incoherent two kinds of situations of crosstalking of Fig. 1 structure, Power penalty and the synoptic diagram that concerns of crosstalking.

Fig. 3 is a structural representation of the present utility model.

Fig. 4 is the relativity synoptic diagram of the utility model structure and existing basic structure coherent crosstalk.

A kind of cascaded fiber grating type optical add-drop multiplexer embodiment of the utility model design as shown in Figure 3, accompanying drawings is as follows:

It is 99% that present embodiment adopts reflectivity, wavelength is two fiber gratings of 1551.88nm, it is the four-port circulator of CIR5 that circulator adopts the model of Shenzhen scientific and technological development incorporated company, and it is the optoisolator composition of ISA5 that isolator adopts the model of Shenzhen scientific and technological development incorporated company.The fiber grating circulator is all done standard fiber joint FC-PC head, connects with flange between each FC-PC head, the middle fiber reel that connects circlewise, all elements all are fixed on the machine plate, constitute one.

The WDM signal that with four tunnel wavelength intervals is 1.6nm carries out road experiment up and down to present embodiment, the DFB-LD directly modulated lasers that four road light sources adopt Wuhan Telecommunication Device Co to make, when obtaining described result and being used for demultiplexing to the rejection ratio of adjacent channel greater than 27dB, obtaining the cascaded fiber grating structure simultaneously compares with basic structure, following road signal the leakage of transmit port reduced 8dB (27dB →-35dB), and the signal of setting out on a journey has obtained complete inhibition to crosstalking of road signal down.

Claims (1)

1. cascaded fiber grating type optical add/drop multiplexer, be included between two circulators and connect first grating with optical fiber, it is characterized in that, in said two circulators, also be connected with second grating, between said first, second grating, also connect an isolator with optical fiber.

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