TW201610496A - Variable optical attenuator with wavelength-dependent loss compensation - Google Patents

Abstract

A variable optical attenuator with wavelength-dependent loss compensation is provided, including: an optical fiber pigtail, a lens, and a reflector, wherein the optical fiber pigtail further comprising at least a first waveguide and a second waveguide; the lens being disposed between the optical fiber pigtail and the reflector for focusing an emitted light from the first waveguide and returning a reflected light from the reflector to the second waveguide of the optical fiber pigtail; and the reflector being disposed at the focus of the lens to reflect the emitted light from the first waveguide passing the lens, and the reflected light passing through the lens to return to the second waveguide, the reflector having an initial position with a normal forming a pre-tilt angle with the axis of lens in the incident plane defined by the two axes, and the reflector tilting towards a larger tilt angle when an attenuation value increasing.

Description

Wavelength dependent loss compensated dimmable attenuator

The disclosure relates to a tunable optical attenuator for wavelength dependent loss compensation.

With the growing demand for communication, the rapid development of a wide range of communication technologies has been promoted. Among them, optical communication has been the focus of more than 20 years. In addition to the deployment of optical fibers, various technologies have been developed to increase the use and efficiency of optical fibers. For example, Wavelength Division Multiplexing (WDM) transmits optical signals of a plurality of different wavelengths to increase transmission capacity.

When tunable optical attenuators are used in fiber WDM systems, a common requirement is to provide consistent attenuation for signals of different wavelengths used. Currently, a variable optical attenuator (VOA) made by combining micro-electro-mechanical-systems (MEMS) wafers and fiber optics is very common. Most MEMS VOAs use tilt mirror technology to achieve optical energy attenuation. That is, an exiting fiber directs light through the small mirror to the other incident fiber. When the small mirror is tilted, part of the light cannot be coupled to the incident fiber, thus producing light attenuation.

Although the mirror-reflective MEMS VOA is quite common on the market, its technical characteristics are not perfect. As the attenuation value increases, different wavelengths have different angles at the same tilt angle. The attenuation value, ie the attenuation value, is wavelength dependent. An indicator called Wavelength dependent loss (WDL) is a measure of the uniformity of attenuation of light of different wavelengths at a certain attenuation value. WDL is used to present the maximum difference in attenuation values at different wavelengths of a certain attenuation value. For example, the expected attenuation value is 20 dB, but in fact the maximum attenuation value is 20.6 dB at 1525 nm and the minimum attenuation is 19.4 dB at 1575 nm, which is called 20 dB. The WDL of the attenuation value is 1.2 dB (= 20.6-19.4). In the commonly used planar mirror-reflective MEMS VOA without WDL compensation, the WDL in the wavelength range of 1525 nm to 1575 nm is about 0.8-1.4 dB at a 20 dB attenuation value. This is because the mode field diameter (MFD) of the long wavelength in the single mode fiber (SMF) is larger than the MFD of the shorter wavelength, so the attenuation of the longer wavelength is smaller than the same displacement of the spot. Attenuation value for shorter wavelengths.

Several developed techniques are used for WDL compensation, and most of these techniques are based on the dispersion properties of the material. At a fixed attenuation value, the displacement of the shorter wavelength spot relative to the fiber is less than the displacement of the longer wavelength to compensate for the MFD. influences. For example, U.S. Patent No. 757, 4096 and U.S. Patent No. 8,280,218 use high dispersion lens materials and alter the angle of grinding of the dual fiber leads to compensate for the WDL. U.S. Patent 7,295,748 employs a wedge pattern to adjust the light path at different wavelengths. When the mirror is activated to increase attenuation, the displacement of the shorter wavelength spot relative to the fiber is less than the displacement of the longer wavelength to compensate for the WDL caused by the difference in MFD.

Embodiments of the present disclosure can provide a tunable optical attenuator for a wavelength dependent loss compensation.

One disclosed embodiment relates to a wavelength dependent loss compensated tunable attenuator comprising: a fiber lead, a lens and a mirror, wherein the fiber lead is a column, one of The end is tapered and connected to the external optical fiber, and the end is a plane having an inclined angle and opposite to the lens, and further includes at least a first waveguide (Waveguide) for emitting light, and a second waveguide for receiving returning light; a columnar body having two front and rear end faces, disposed between the fiber lead and the mirror, for focusing the light emitted by the first waveguide of the fiber lead and returning the reflected light to the second waveguide of the fiber lead; The mirror is placed on the focal length of the lens for reflecting the incident light emitted from the first waveguide and passing through the lens, and the light is reflected and then returned to the second waveguide through the lens. The normal line of the initial position of the mirror and the axis of the lens A tilt angle is formed and on the plane of incidence defined by the two axes, when the attenuation value is large, the mirror is tilted in the direction of increasing the tilt angle.

Another embodiment disclosed is directed to a wavelength dependent loss compensated dimming attenuator comprising a collimator and a mirror, wherein the photoreceptor comprises a fiber lead and a lens; the fiber lead And the lens is fixed by a tubular housing, and the optical fiber lead includes at least a first waveguide and a second waveguide; the lens is used to focus the light emitted by the first waveguide of the optical fiber lead and return the reflected light to the optical fiber lead a second waveguide; the mirror is placed on the focal length of the lens to reflect the incident light emitted from the first waveguide and passing through the lens, and the light is reflected and then returned to the second waveguide through the lens, the normal of the initial position of the mirror and the lens The axis lines form an oblique angle and are on the plane of incidence defined by the two axes, and when the attenuation value is large, the mirror is inclined in the direction of increasing the inclination angle.

The above and other advantages of the present disclosure will be described in detail below with reference to the following drawings, detailed description of the embodiments, and claims.

21‧‧‧Mirror

22‧‧‧ lens

23‧‧‧Fiber lead

24‧‧‧Incoming fiber

25‧‧‧Injecting fiber core

26‧‧‧Output fiber core

27‧‧‧Output fiber

28‧‧‧Long wavelength spot

29‧‧‧Short-wavelength spots

The first A diagram and the first B diagram are schematic diagrams consistent with an disclosed embodiment, illustrating a Wavelength dependent loss compensated dimmable attenuator.

The second A diagram and the second B diagram are schematic diagrams consistent with an disclosed embodiment, illustrating the dimming attenuators of the first A diagram and the first B diagram. When the attenuation value is large, the mirrors are enlarged. The direction of the tilt angle is inclined.

The third to seventh figures are schematic views consistent with an embodiment of the disclosure, illustrating the variation of WDL with attenuation values under different pretilt angles θ for different lens materials and focal lengths.

Embodiments of the present disclosure can provide a tunable optical attenuator for a wavelength dependent loss compensation.

The first A diagram and the first B diagram are schematic diagrams consistent with an disclosed embodiment, illustrating a wavelength dependent loss compensated dimming attenuator. As shown in FIG. B, the wavelength dependent loss compensated tunable attenuator includes a fiber lead 23, a lens 22, and a mirror 21, wherein the mirror 21 is driven by a MEMS actuator (not shown). ). The fiber lead 23 includes at least one exit fiber 27 and an incident fiber 24, wherein the exit fiber 27 further includes an exit fiber core 26, the incident fiber 24 further comprising an incident fiber core 25, when light passes from the exit fiber 27 through the lens 22, the light Reflected by the MEMS driven mirror 21. The axis of the lens 22 forms a pretilt angle θ with the normal to the lens 21 and is on the plane of incidence defined by the two axes. The reflected light enters the incident fiber 24 through the lens 22. As shown in the minimum attenuation state, the reflected light is focused, forming a longer wavelength spot 28 near the incident fiber core 25, and a shorter wavelength spot 29, as shown in Figure A. Referring to the first A map, the pretilt angle θ causes the longer wavelength spot 28 and the shorter wavelength spot 29 to be eccentric to compensate for the WDL caused by the difference in the MFD. As shown in the first B diagram, the lens 22 is disposed between the optical fiber lead 23 and the reflection plate 21.

It should be noted that the optical fiber lead 23 includes at least a first waveguide (incident optical fiber) and a second waveguide (exit optical fiber). One end of the fiber lead 23 facing the lens 22 is an inclined surface to form a gap with the corresponding inclined surface of the lens 22. The other end of the lens 22 has a dome shape toward the mirror 21. The mirror 21 is disposed at an initial position at a pre-tilt angle θ at the normal to the lens 21 and the axis of the lens 22 and on the plane of incidence defined by the two axes. In operation, as the attenuation value increases, the MEMS actuator tilts the drive mirror 21 toward a greater tilt angle, as shown in the second B, where the normal to mirror 21 and the axis of lens 22. The line forms a tilt angle θ + Δθ and is on the plane of incidence defined by the two axes.

As mentioned earlier, the mirror is driven to cause a given attenuation. As shown in the second B diagram, the mirror 21 is tilted toward a greater angle such that the axis of the lens 22 forms a pretilt angle θ + Δθ with the normal to the lens 21 and on the plane of incidence defined by the two axes. This angle causes the longer wavelength spot 28 and the shorter wavelength spot 29 to be more eccentric to compensate for the larger WDL caused by the difference in MFD at larger attenuation values, as shown in Figure 2A.

It should also be noted that the lens 22 can be embodied in a variety of forms. For example, lens 22 can be a convex lens having a first surface and a second surface, and at least one surface of the two surfaces is a curved surface for focusing light. The lens 22 may also be a C-lens having a columnar shape of a first end surface and a second end surface, the first end surface being an inclined surface and the second end surface being a curved surface, and the second end surface may be Focus on light. The lens 22 can also be a Grin lens having an optical axis and the index of refraction changes in the radial direction, and the light can be focused via a change in refractive index.

Depending on the MFD characteristics of the fiber and the dispersion characteristics of the material and the focus specifications of the lens, the WDL can be optimized by adjusting the value of θ over a given attenuation range.

The spot size w is half of the MFD and has a linear relationship with the wavelength in a small wavelength range (for example, the C band or the L band), and the spot size w can be expressed as follows: w = a + b * λ where λ is Wavelength, a is a constant and b is a linear dispersion coefficient. The most representative fiber is the SMF-28e XB, which conforms to the ITU G657A standard for single-mode fiber, and has a b value of 2.5 um/um. After the light is emitted from the fiber, the energy of the light is Gaussian. For optimal coupling (non-attenuation), the core 25 at the inclined surface of the fiber lead 23 is at the back focal length of the lens 22. When the rotating mirror 21 to cause the reflected light with respect to the fiber core 25 is displaced, the insertion loss variation AIL can be expressed as follows: ΔIL (λ) = 4.34 * [x / w (λ)] 2 where x is the displacement of the reflected light. The reason for the WDL is because the different wavelengths λ have different w (or MFD) and produce different ΔIL. And WDL can be expressed as follows:

Where Δλ is a given bandwidth for estimating WDL and n is the refractive index of the lens at the center wavelength. Further, dn/d λ represents the dispersion of the refractive index close to the center wavelength, and is a negative value for a general material. As in the above equation, the second term in parentheses represents the WDL caused by the difference in MFD of different wavelengths, and the first term in parentheses is the compensation term caused by the shift of the reflected light of different wavelengths. In reality, the displacement of shorter wavelength spots relative to the fiber will be longer than the long wavelength spot. The displacement is smaller, that is, the longer and shorter wavelength spots are relatively eccentric to compensate for the WDL caused by the difference in MFD. Therefore, as long as the lens material exhibits excellent dispersion characteristics and the appropriate pretilt angle θ of the mirror 21 is selected within a given attenuation range, it can be optimized by compensating for the compensation term (first term) of the essential WDL (second term). WDL. Further, the larger the dispersion (|dn/d λ|) of the lens material, the smaller the pretilt angle θ required for WDL optimization.

Most lens materials exhibit a longer wavelength dispersion characteristic and a smaller refractive index than a shorter wavelength (dn/d λ < 0), for example, NSF11 used in a C-lens has a refractive index n (1550 nm) = 1.743, dn /d λ(1550nm)=-0.0180um ^-1 , and NPH2 has a refractive index n(1550nm)=1.861, dn/d λ(1550nm)=-0.0247um ^-1 , and less common Si has a refractive index n( 1550 nm) = 3.478, dn / d λ (1550 nm) = -0.0823 um ^-1 .

Depending on the limit of the pretilt angle and the size of the MEMS mirror, a suitable focal length of the lens can be determined. The curvature of the lens using different materials can also be determined. Regardless of the lens material and focal length, the WDL can be optimized via a pre-tilt angle θ adjustment to compensate for MFD changes with respect to wavelength for a given attenuation range.

The third to seventh figures are schematic views consistent with an embodiment of the disclosure, illustrating the variation of WDL with attenuation values under different pretilt angles θ for different lens materials and focal lengths. The third figure illustrates the change of WDL with the attenuation value under different tilt angles θ when NSF11 is used as the lens material and the focal length (FL) is 2.0 mm. As shown in the third figure, when the set attenuation value ranges from 0 to 20 dB, and the WDL (1575 nm differential loss - 1525 nm differential loss) requirement is less than ±0.2 dB, the optimum value of the tilt angle θ is about 3.8°. When the WDL requirement is less than ±0.3 dB, the tilt angle θ ranges from about 3.0 to 5.4. The illustration below shows the different lenses Material and focal length, WDL varies with attenuation due to different pretilt angles θ (ranging from 0 to 30 dB).

The fourth figure illustrates the change in WDL with attenuation values under different θ conditions when NSF11 is used as the lens material and FL = 2.4 mm. When the set attenuation value ranges from 0 to 20 dB, and the WDL requirement is less than ±0.2 dB, θ is approximately 3.5°.

The fifth graph illustrates the change in WDL with attenuation values under different θ conditions when NSF11 is used as the lens material and FL = 1.6 mm. When the set attenuation value ranges from 0 to 20 dB, and the WDL requirement is less than ±0.2 dB, θ is approximately 4.8°.

The sixth graph illustrates the change in WDL with attenuation values under different θ conditions when Si is used as the lens material and FL = 2.0 mm. When the set attenuation value ranges from 0 to 20 dB, and the WDL requirement is less than ±0.2 dB, θ is approximately 2.4°.

The sixth graph illustrates the change in WDL with attenuation values under different θ conditions when NPH2 is used as the lens material and FL = 2.0 mm. When the set attenuation value ranges from 0 to 20 dB, and the WDL requirement is less than ±0.2 dB, θ is approximately 3.0°.

As shown in the above figures, for the same lens material, the longer the FL, the smaller the pretilt angle θ is needed to optimize the WDL. Similarly, for the same FL, the larger the dispersion of the lens material (|dn/d λ|), the smaller the pretilt angle θ is needed to optimize the WDL.

Therefore, in practical applications, as long as the lens material and FL are known, the required WDL optimized pretilt angle θ can be determined. In addition, two methods can be used to achieve the light emission direction of the collimator (the lens and the optical fiber lead) forming a pretilt angle θ with the axis of the lens. The first method is to position the fiber at the back focus and then shift the fiber lead in the radial direction to achieve the desired pretilt angle θ. The second method is to adjust the length of the lens or the fiber lead and lens The inclined angle of the inclined surface is to achieve the desired emission angle θ, and the fiber lead and the lens are placed in the glass tube.

In practical applications, the present invention can be implemented in two modes. The first mode is referred to as a normally open, or bright mode; the second mode is commonly referred to as a normally closed, or dark mode. The normally open mode is defined as follows: When the mirror is not driven, the attenuation value is minimal and the normal to the mirror forms an oblique angle θ with the axis of the lens. When it is desired to increase the attenuation value, the mirror is driven to tilt in a direction that forms a tilt angle of θ + Δθ. On the other hand, the normally closed mode is defined as follows: when the mirror is not driven, the attenuation value is maximum, and the normal to the mirror forms an oblique angle θ + Δθ with the axis of the lens. When it is desired to reduce the amount of attenuation, the mirror is driven to tilt in a direction that forms a θ tilt angle. Whether in the bright or dark mode, as long as the attenuation of the mirror is such that the axis of the lens on the plane of incidence forms a large angle with the normal to the mirror, this can compensate for wavelength dependent losses. However, this incident plane is not limited to a specific direction as long as the pretilt angle θ and the attenuation tilt angle Δθ of the mirror are both inclined at the same incident plane.

The above is only the embodiment of the disclosure, and the scope of the disclosure is not limited thereto. All changes and modifications made to the scope of the patent application of the present invention are intended to fall within the scope of the invention.

21‧‧‧Mirror

22‧‧‧ lens

23‧‧‧Fiber lead

24‧‧‧Incoming fiber

25‧‧‧Injecting fiber core

26‧‧‧Output fiber core

27‧‧‧Output fiber

Claims (12)

A wavelength dependent loss compensated tunable optical attenuator comprising: a fiber lead, a lens and a mirror; wherein the fiber lead is a columnar body, one end of which is tapered and connected to the external fiber, and the other end is a plane of the tilt angle and opposite to the lens, further comprising at least a first waveguide for emitting light, and a second waveguide for receiving return light; the lens being a columnar body having two front and rear end faces, Between the fiber lead and the mirror, for focusing the light emitted by the first waveguide of the fiber lead and returning the reflected light to the second waveguide of the fiber lead; the mirror is placed At a focal length of the lens, for reflecting incident light emitted from the first waveguide and passing through the lens, the light is reflected and then returned to the second waveguide through the lens, the normal of the initial position of the mirror and the axis of the lens The line forms an oblique angle and is incident on the plane defined by the two axes, and when the attenuation value is large, the mirror is inclined in a direction in which the inclination angle is increased. The wavelength-dependent loss compensated tunable attenuator of claim 1, wherein the lens is a convex lens having a first end surface and a second end surface, and at least one of the two end faces is used for focusing a curved surface. The wavelength-dependent loss compensated tunable attenuator according to claim 1, wherein the lens is a C-lens having a columnar shape of a first end surface and a second end surface, the first end surface An inclined surface and the second end surface are a curved surface, and the second end surface can focus the light. A wavelength-dependent loss compensated tunable attenuator as described in claim 1, wherein the lens is a Grin lens having an optical axis and the refractive index changes in a radial direction, and the light can be changed via a refractive index Focus. The wavelength dependent loss compensated tunable optical attenuator of claim 1, wherein the normal of the mirror forms an oblique angle with the axis of the lens and is on the plane of incidence defined by the two axes, And the tilt angle is such that the displacement of the shorter wavelength spot relative to the fiber is smaller than the displacement of the longer wavelength spot, that is, the longer and shorter wavelength spots are relatively eccentric to compensate for the WDL caused by the difference in MFD. The wavelength dependent loss compensated tunable optical attenuator of claim 1, wherein the normal of the mirror forms an oblique angle with the axis of the lens and is on the plane of incidence defined by the two axes, And the angle of inclination ranges from 1° to 10°. A wavelength dependent loss compensated tunable optical attenuator comprising a collimator and a mirror, wherein the optical comparator comprises a fiber lead and a lens; the optical fiber lead and the lens are formed by a tubular outer casing (Housing) fixed, and the fiber lead includes at least a first waveguide and a second waveguide; the lens is used to focus the light emitted by the first waveguide of the fiber lead and return the reflected light to the fiber lead a second waveguide; the mirror is disposed at a focal length of the lens to reflect incident light emitted from the first waveguide and passing through the lens, and the light is reflected and returned to the second waveguide through the lens, the mirror is initially The normal of the position forms an oblique angle with the axis of the lens and on the plane of incidence defined by the two axes, and when the attenuation value is large, the mirror is tilted in a direction that increases the angle of inclination. A wavelength-dependent loss compensated dimming attenuator as described in claim 7 wherein the lens is a convex lens having a first end surface and a second end surface, and at least one of the end faces is for focusing a curved surface. The wavelength-dependent loss compensated dimming attenuator according to claim 7, wherein the lens is a C-lens having a columnar shape of a first end surface and a second end surface, the first end surface An inclined surface and the second end surface are a curved surface, and the second end surface can focus the light. The tunable attenuator of claim 7, wherein the lens is a Grin lens having an optical axis and the refractive index changes in a radial direction, and the light can be focused via a change in refractive index. A wavelength-dependent loss compensated tunable attenuator as described in claim 7 wherein the normal to the mirror forms an oblique angle with the axis of the lens and on the plane of incidence defined by the two axes, And the tilt angle is such that the displacement of the shorter wavelength spot relative to the fiber is smaller than the displacement of the longer wavelength spot, that is, the longer and shorter wavelength spots are relatively eccentric to compensate for the WDL caused by the difference in MFD. A wavelength-dependent loss compensated tunable attenuator as claimed in claim 7 wherein the normal to the mirror forms an oblique angle with the axis of the lens and on the plane of incidence defined by the two axes, And the angle of inclination ranges from 1° to 10°.