CN101963685A - Variable optical attenuator capable of compensating WDL by adjusting optical waveguide position - Google Patents

Abstract

The invention relates to a variable optical attenuator based on a reflecting mirror, in particular to a wavelength dependent loss (WDL) compensation variable optical attenuator capable of compensating the wavelength dependent loss by adjusting the optical waveguide position. In a reflecting variable optical attenuator (VOA) system, through adjusting the position of the input optical waveguide on an input surface and the position of the output optical waveguide on an output surface, the transmission path of the light beam containing different wavelength components in a lens, chromatic dispersion generated by the lens self is increased, and the wavelength dependent loss (WDL) is compensated.

Description

By adjusting the adjustable optical attenuator that the optical waveguide position compensates WDL

Technical field

The present invention relates to a kind of adjustable optical attenuator (Variable Optical Attenuator based on catoptron, VOA) system, relate in particular to the wavelength dependent loss compensation variable optical attenuator, it takes to change the position of input waveguide and output optical waveguide, increase system dispersion, compensate Wavelength Dependent Loss (WDL) thus.

Background technology

Fig. 1 a, 1b show common reflective VOA basic structure.Fig. 1 a is an IL situation hour in the prior art, and Fig. 1 b is the situation during attenuation state in the prior art.As shown in Figure 1a, common reflective VOA comprises: lens, catoptron, input waveguide, output optical waveguide.The reflection back takes place by catoptron and forms folded light beam in the light beam scioptics collimation that contains the different wave length composition from output optical waveguide comes out again.Folded light beam scioptics again focuses on output optical waveguide.When catoptron was setovered certain angle, folded light beam was inserted loss (Insertion loss IL) with minimum and is coupled into output optical waveguide.Shown in Fig. 1 b, when catoptron increases or reduces angle of eccentricity, there is the partial reflection light beam to deflect away from optical waveguide, reduce coupling efficiency, thereby formed the decay output of luminous energy.

Yet the optical attenuator of this structure has and a kind ofly is called Wavelength Dependent Loss (Wavelengthdependent loss, shortcoming WDL) can influence the attenuation accuracy of device, even the signal to noise ratio (S/N ratio) of light signal etc.

Luminous energy is coupled into the efficient of optical waveguide and follows following factor relevant, comprise: the mode field diameter of the angle of the side-play amount at spot center and optical waveguide center, the incident angle of coupled light beam, optical waveguide end face, the radius of optical waveguide and incident light (Mode field diameter, MFD) etc.The reflected light optical attenuator belongs to co-structured, the angle of the incident angle of coupled light beam, optical waveguide end face and the radius of optical waveguide are only relevant with the mode field diameter of the offset distance at coupling light spot center and optical waveguide center and coupling light to the pad value of decay, and offset distance all follows the light wavelength that is coupled relevant with mode field diameter simultaneously.In certain wavelength coverage, when the optical attenuator catoptron was setovered certain angle, the difference of different wave length loss value was referred to as Wavelength Dependent Loss, WDL.

As everyone knows, insert the function that loss IL can be expressed as wavelength, shown in following equation (1):

$\mathrm{IL}\left(\mathrm{\λ}\right)=-4.343\·{\left(\frac{x\left(\mathrm{\λ}\right)}{\mathrm{\ω}\left(\mathrm{\λ}\right)}\right)}^2---\left(1\right)$

Wherein ω (λ) is the coupling light spot size, for MFD half, is the function of wavelength X; X (λ) is coupling light spot center and optical waveguide center offset, and it is mainly determined by mirror angle, and is simultaneously also relevant with wavelength X.

In the small wavelength scope, as optical communication system commonly used C and L-band, ω (λ) can linear approximate relationship, is expressed as equation (2):

ω(λ)＝a+b·λ (2)

Wherein, a, b are constant coefficient.WDL is expressed as equation (3)

$\mathrm{WDL}\left(\mathrm{\λ}\right)=\frac{d\left[\mathrm{IL}\left(\mathrm{\λ}\right)\right]}{\mathrm{d\λ}}=-4.343\·2\·\frac{x\left(\mathrm{\λ}\right)}{{\mathrm{\ω}}^3\left(\mathrm{\λ}\right)}\·[\frac{d\left[x\left(\mathrm{\λ}\right)\right]}{\mathrm{d\λ}}\·\mathrm{\ω}\left(\mathrm{\λ}\right)-b\·x\left(\mathrm{\λ}\right)]---\left(3\right)$

$D\left(\mathrm{\λ}\right)=\frac{d\left[x\left(\mathrm{\λ}\right)\right]}{\mathrm{d\λ}}---\left(4\right)$

In certain wavelength coverage, as C Band and L Band, WDL can be expressed as

$\mathrm{WDL}=2\·\mathrm{IL}\·(\frac{D}{x}-\frac{b}{\mathrm{\ω}})\·\mathrm{\Δ\λ}---\left(5\right)$

Wherein Δ λ is a wavelength difference, D be twice of described light beam by the dispersion measure behind the described lens, also be the difference of described offset distance in certain wave band.The common VOA that does not do compensation, the chromatic dispersion behind the input light scioptics is very little, and device is when certain pad value, and the b constant coefficient is the WDL main affecting factors.

At present, the technical scheme that has had some to solve the reflective VOA WDL of system problem, but all there are various defectives.Adopt as U.S.'s publication (US2007/0031104A1) to add dispersed light and compensate WDL, need to add assembly, do not consider the dispersion characteristics of lens self.And U.S.'s publication (US2004/0008967A1) is not parallel to lensed endface by Waveguide end face and regulate the axial orientation of waveguide with respect to lens, to obtain minimum WDL.Here do not consider that position adjustment changes chromatic dispersion and compensates the influence of MFD to WDL.

In view of this, demand proposing a kind of adjustable optical attenuator that compensates Wavelength Dependent Loss by adjustment optical waveguide position urgently.

Summary of the invention

At the many drawbacks that exist in the prior art, the present invention proposes a kind of by adjusting the adjustable optical attenuator that position, optical waveguide position compensates Wavelength Dependent Loss.

The objective of the invention is by change input waveguide in position on the input face and output optical waveguide the position in output face, thereby change the transmission path of light beam in lens that comprises the different wave length composition, increase compensates Wavelength Dependent Loss (WDL) by the chromatic dispersion that lens self produce.

In order to achieve the above object, the invention provides a kind of wavelength dependent loss compensation variable optical attenuator, comprising:

Input waveguide, emission comprises the light beam of different optical wavelength compositions, has axis 1, can 1 any vertical direction move along the axis;

Output optical waveguide receives the described light beam that comprises different optical wavelength compositions, has axis 2, can 2 any vertical direction move along the axis;

Lens, has optical axis 3, be used for collimation from described input waveguide emitted light beams, and the light beam after mirror reflects focused on described output optical waveguide, and described light beam is produced in various degree chromatic dispersion according to the position of the position of described input waveguide and output optical waveguide;

The catoptron at adjustable angle of inclination, be used to receive light beam from described lens, and described light beam is passed described lens arrive described output optical waveguide, the different inclination angle of described catoptron makes attenuator produce the pad values of different sizes, and produces certain Wavelength Dependent Loss (WDL) when making certain pad value.

According to a preferred embodiment of the invention, wherein adjust input waveguide and output optical waveguide position, allow axis 1, axis 2 and 3 three line parallels of optical axis, and make axis 1 leave the certain distance of optical axis (d1), the certain distance of optical axis (d2) is left in axis 2, change described light beam travel path in described lens, the chromatic dispersion that increase is produced by described lens self, when making the light of described light beam heterogeneity with the coupling of described output optical waveguide spot center and optical waveguide center have different offset distances from, compensate Wavelength Dependent Loss (WDL).

According to a preferred embodiment of the invention, the wherein said input waveguide input optical fibre that is adjustable position.

According to a preferred embodiment of the invention, the wherein said output optical waveguide output optical fibre that is adjustable position.

According to a preferred embodiment of the invention, wherein said output optical fibre has fibre core and coat.

According to a preferred embodiment of the invention, wherein said catoptron comprises reflection mirror photoswitch.

According to a preferred embodiment of the invention, wherein said reflection mirror photoswitch comprises MEMS (micro electro mechanical system) (Micro Electro-Mechanical Systems, MEMS) photoswitch or traditional mechanical formula photoswitch.

According to a preferred embodiment of the invention, wherein said reflection mirror photoswitch comprises reflection mirror wavelength-selective switches (WSS).

According to a preferred embodiment of the invention, wherein said lens are the C-lens lens.

According to a preferred embodiment of the invention, wherein said lens are G-lens lens or other collimation lenses.

The present invention can be in reflective adjustable optical attenuator (VOA) system, by adjust input waveguide in position on the input face and output optical waveguide the position in output face, thereby change the transmission path of light beam in lens that comprises the different wave length composition, increase comes the loss (WDL) of compensated wave long correlation by the chromatic dispersion that lens self produce.

Though will describe the present invention in conjunction with some exemplary enforcements and using method hereinafter, and it will be appreciated by those skilled in the art that and be not intended to the present invention is limited to these embodiment.Otherwise, be intended to cover all substitutes, correction and the equivalent that are included in defined spirit of the present invention of appending claims and the scope.

Other advantages of the present invention, target, to set forth in the following description to a certain extent with feature, and to a certain extent,, perhaps can obtain instruction from the practice of the present invention based on being conspicuous to those skilled in the art to investigating hereinafter.Target of the present invention and other advantages can be passed through following instructions, claims, and the specifically noted structure realizes and obtains in the accompanying drawing.

Description of drawings

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is described in further detail below in conjunction with accompanying drawing, wherein:

Fig. 1 a is an IL reflective VOA basic block diagram hour in the prior art;

Fig. 1 b is the reflective VOA basic block diagram during attenuation state in the prior art;

Fig. 2 a shows according to the VOA figure that adjusts the waveguide position that has of the present invention;

Fig. 2 b shows the situation figure when the VOA that has the adjustment of waveguide position according to the present invention is in attenuation state;

Fig. 3 a is the dispersion compensation figure after example explanation the present invention adjusts the optical waveguide position with c-lens;

Fig. 3 b shows when adjusting after the fiber position VOA attenuation state, the distribution plan of output optical fibre end different wave length hot spot;

After Fig. 4 shows compensation optimizing, with the VOA that does not optimize design sketch relatively;

Fig. 5 shows the schematic diagram that described lens adopt G-lens.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described in further detail.It should be noted that according to of the present invention by adjusting the embodiment of adjustable optical attenuator that position, optical waveguide position compensates Wavelength Dependent Loss, but the invention is not restricted to this embodiment as just example.

Hereinafter, the technical conceive instantiation mode of the VOA compensation WDL among the present invention will be described in detail.

Shown in Fig. 2 a, VOA according to the present invention comprises: the input optical fibre of adjustable position, the lens with optical axis 3, tiltable catoptron, and the output optical fibre that has fibre core and coat of adjustable position.Situation when Fig. 2 b shows the VOA that has the adjustment of waveguide position according to the present invention and is in attenuation state, this moment, the angle of catoptron was different.By catoptron among Fig. 2 a is changed certain angle of eccentricity, import optical attenuation output thereby make.

Shown in Fig. 2 a and 2b, this wavelength dependent loss compensation variable optical attenuator comprises: input waveguide, and emission comprises the light beam of different optical wavelength compositions, has axis 1, can 1 any vertical direction move along the axis; Output optical waveguide receives the described light beam that comprises different optical wavelength compositions, has axis 2, can 2 any vertical direction move along the axis; Lens, has optical axis 3, be used for collimation from described input waveguide emitted light beams, and the light beam after mirror reflects focused on described output optical waveguide, and described light beam is produced in various degree chromatic dispersion according to the position of the position of described input waveguide and output optical waveguide; The catoptron at adjustable angle of inclination, be used to receive light beam from described lens, and described light beam is passed described lens arrive described output optical waveguide, the different inclination angle of described catoptron makes attenuator produce the pad values of different sizes, and produces certain Wavelength Dependent Loss (WDL) when making certain pad value.

Wherein adjust input waveguide and output optical waveguide position, allow axis 1, axis 2 and 3 three line parallels of optical axis, and to make axis 1 be d1 to the distance of optical axis, axis 2 is d2 to the distance of optical axis, change described light beam travel path in described lens, increase is by the chromatic dispersion that described lens self produce, when making the light of described light beam heterogeneity be coupled with described output optical waveguide spot center and optical waveguide center have different offset distances from, compensate WDL.

According to a preferred embodiment of the invention, the wherein said input waveguide input optical fibre that is adjustable position; Described output optical waveguide is the output optical fibre of adjustable position, and described output optical fibre can also have fibre core and coat.

According to a preferred embodiment of the invention, described catoptron also comprises reflection mirror photoswitch, can have MEMS (micro electro mechanical system) (Micro Electro-Mechanical Systems, MEMS) or two kinds of traditional mechanical formulas.Can also be based in addition the reflection mirror wavelength-selective switches (wavelength selective switch, WSS).

The common VOA that does not do compensation, input optical fibre and output optical fibre are roughly placed along optical axis 3 symmetries, light path is roughly conjugated structure, so it is very little through the dispersion measure behind the lens to comprise the light beam of different wave length composition, the distance that the hot spot that promptly is coupled deflects away from the output optical fibre center is also very little with the wavelength variations rate.According to equation (5)

$\mathrm{WDL}=2\·\mathrm{IL}\·(\frac{D}{x}-\frac{b}{\mathrm{\ω}})\·\mathrm{\Δ\λ}$

In order to compensate WDL, in the present invention, making input optical fibre is d1 from the distance of optical axis 3, and output optical fibre is d2 from the distance of optical axis 3, changes the travel path of described light beam in lens, increases the chromatic dispersion D of lens self.

Compared with prior art, the common VOA that does not do compensation, the input and output optical waveguide roughly is symmetrically distributed along optical axis 3, the intersection point of central ray and lens sphere also roughly is symmetrically distributed along optical axis 3, cause sphere to almost not contribution of light beam chromatic dispersion, and behind offset d 1 and the d2, described intersection point asymmetric distribution, sphere increases the contribution to dispersion compensation.

[source of chromatic dispersion is described]

According to the present invention, it is that a kind of radius-of-curvature is the embodiment of the C-lens of R that Fig. 3 a has described described lens.The input optical fibre center is d1 from optical axis 3 length in the diagram, the input optical fibre center is d2 from optical axis 3 length, behind the catoptron biasing certain angle, comprise the incident beam of different wave length composition, for example 1525nm and 1570nm, penetrate after the C-lens collimation from input optical fibre, arrive the catoptron back reflection, focus on output optical fibre coupling output by C-lens again, after the mirror angle fine adjustment, coupling hot spot centre distance skew output optical fibre center makes VOA produce certain pad value.Described light beam can produce chromatic dispersion when propagating in C-lens, the dispersion compensation piece shown in Fig. 3 a can be used as equivalent and calculates dispersion measure D, and when d1 and d2 differ hour, the dispersion compensation piece is approximately the Xi shape sheet that angle is α, can be expressed as

$\mathrm{\&alpha;}=\frac{\sqrt{R^2-d{2}^2}-\sqrt{R^2-{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="H2009100895133E0000041.png"\; state="\{\{state\}\}">d</figure-callout>}1}^2}}{d1-d2}---\left(6\right)$

$D=2\&times;\mathrm{\&alpha;}\&times;f\&times;\frac{\mathrm{\&Delta;n}}{\mathrm{\&Delta;\&lambda;}}---\left(7\right)$

Wherein f is the focal length of c-lens, and n is the refractive index of lens.

[result that chromatic dispersion causes]

Fig. 3 b has described the output optical fibre sectional view that has fibre core, and the mirror tilt angle slightly changes the effect that the back is produced 1525nm hot spot and 1570nm hot spot respectively by the described equivalent dispersion compensation module of Fig. 3 a.Wherein X1 is short wavelength's composition hot spot (as 1525nm), and X2 is long wavelength's composition hot spot (as 1570nm).The equivalence dispersion compensation module makes the distance of described two kinds of light components coupling hot spot off-centring optical fiber unequal according to (as 1525nm) composition of the long wavelength in the wavelength separated input beam and short wavelength (as 1570nm) composition.Wherein short wavelength (as 1525nm) hot spot leans on output optical fibre centre distance more closely, and long wavelength (as 1570nm) hot spot leans on output optical fibre centre distance far; Short wavelength (as 1525nm) light MFD is less than long wavelength (as 1570nm) light MFD simultaneously.According to equation (1), described offset distance is compared with MFD, and is opposite to the influence of WDL.Like this, the difference of the described offset distance that is caused by equivalent chromatic dispersion piece has compensated the WDL that is caused by MFD difference at least in part.

After changing the position of skew optical axis 3 of described two kinds of optical fiber, promptly the WDL after the compensation can be expressed as

$\mathrm{WDL}=2\&CenterDot;\mathrm{IL}\&CenterDot;(\frac{\sqrt{R^2-d{2}^2}-\sqrt{R^2-{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="H2009100895133E0000041.png"\; state="\{\{state\}\}">d</figure-callout>}1}^2}}{(d1-d2)\&CenterDot;x}\&CenterDot;2\&CenterDot;f\&CenterDot;\frac{\mathrm{\&Delta;n}}{\mathrm{\&Delta;\&lambda;}}-\frac{b}{\mathrm{\&omega;}})---\left(8\right)$

Wherein Δ λ is the wavelength difference of selected wavelength coverage, and Δ n is the refringence of light when c-lens propagates in the selected wavelength coverage.When selecting suitable optical fiber offset distance d1 and d2, can making on a large scale, the interior WDL of attenuation range reduces to very little.

Make WDL littler, make WDL=0, can obtain

$\arcsin \left(\frac{d1}{R}\right)\text{+arcsin}\left(\frac{d2}{R}\right)=\mathrm{\&pi;}-2\&CenterDot;\arcsin \left(\frac{1}{\sqrt{1+{\left(\frac{b\&CenterDot;\mathrm{\&Delta;\&lambda;}\&CenterDot;x}{2\&CenterDot;f\&CenterDot;\mathrm{\&omega;}\&CenterDot;\mathrm{\&Delta;n}}\right)}^2}}\right)---\left(9\right)$

As long as satisfy the d1 and the d2 of (9) formula, can compensate WDL.Because the offset distance x difference under the different I L situation can not all be reduced to 0 to the WDL of all IL, but select suitable d1 and d2, can make the WDL in the high attenuation scope reduce to very little.

Fig. 4 shows the WDL of the VOA that fiber position of the present invention adjusts, and with the WDL of the VOA that does not add compensation relatively, to increase the compensation effect of lens self chromatic dispersion be significant in the present invention as can be seen.

[mode that G-lens realizes]

As shown in Figure 5, the present invention can also realize with the mode that G-lens or other collimation lenses replace C-lens.The G-lens of graded index can equivalence be the lens of homogeneous refractive index, and as accompanying drawing 5, when input optical fibre and output optical fibre departed from each optical axis certain distance, light beam also increases lens self behind the G-lens path changing chromatic dispersion compensated WDL.

The above is the preferred embodiments of the present invention only, is not limited to the present invention, and obviously, those skilled in the art can carry out various changes and modification and not break away from the spirit and scope of the present invention the present invention.Like this, if of the present invention these are revised and modification belongs within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also is intended to comprise these changes and modification interior.

Claims (10)

1. one kind by adjusting the adjustable optical attenuator that the optical waveguide position compensates Wavelength Dependent Loss, comprising:

Input waveguide, emission comprises the light beam of different optical wavelength compositions, has axis 1, can 1 any vertical direction move along the axis;

Output optical waveguide receives the described light beam that comprises different optical wavelength compositions, has axis 2, can 2 any vertical direction move along the axis;

Lens, has optical axis 3, be used for collimation from described input waveguide emitted light beams, and the light beam after mirror reflects focused on described output optical waveguide, and described light beam is produced in various degree chromatic dispersion according to the position of the position of described input waveguide and output optical waveguide; And

The catoptron at adjustable angle of inclination, be used to receive light beam from described lens, and described light beam is passed described lens arrive described output optical waveguide, the different inclination angle of described catoptron makes attenuator produce the pad values of different sizes, and produces certain Wavelength Dependent Loss (WDL) when making certain pad value.

2. adjustable optical attenuator according to claim 1, wherein adjust input waveguide and output optical waveguide position, allow axis 1, axis 2 and 3 three line parallels of optical axis, and make axis 1 leave the certain distance of optical axis (d1), the certain distance of optical axis (d2) is left in axis 2, thereby change the travel path of described light beam in described lens, the chromatic dispersion that increase is produced by described lens self, when making the light of described light beam heterogeneity with the coupling of described output optical waveguide spot center and optical waveguide center have different offset distances from, compensate WDL.

3. adjustable optical attenuator according to claim 1 and 2 is characterized in that described input waveguide is the input optical fibre of adjustable position.

4. adjustable optical attenuator according to claim 1 and 2 is characterized in that described output optical waveguide is the output optical fibre of adjustable position.

5. adjustable optical attenuator according to claim 4 is characterized in that described output optical fibre has fibre core and coat.

6. adjustable optical attenuator according to claim 1 is characterized in that described catoptron comprises reflection mirror photoswitch.

7. adjustable optical attenuator according to claim 6 is characterized in that described reflection mirror photoswitch comprises MEMS (micro electro mechanical system) (MEMS) photoswitch or traditional mechanical formula photoswitch.

8. adjustable optical attenuator according to claim 6 is characterized in that described reflection mirror photoswitch comprises reflection mirror wavelength-selective switches (WSS).

9. adjustable optical attenuator according to claim 1 and 2, wherein said lens are the C-lens lens.

10. adjustable optical attenuator according to claim 1 and 2, wherein said lens are G-lens lens or other collimation lenses.

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