JP2001512244A - Grating-based coupler device - Google Patents

Abstract

Abstract: An add / drop filter for light wave energy (10) is a very thin body region (12) defined by the combined length of drawn optical fibers (30, 31, 34, 35). A Bragg grating (27). Light propagates through the barrel region via the adiabatic tapered fibers (20, 21, 24, 25) and within the body's air-glass waveguide, two orthogonally adjacent fibers from two longitudinally adjacent fibers. Mode and is reflected from one fiber to the other. Due to the cross section of the torso region (12), the reflected drop wavelength is polarization independent, it has no loss peak in the wavelength range of interest. The back reflection is shifted outside the target wavelength width. High performance gratings are written with the body region of the fiber sensitized. The narrow spectral bandwidth grating provides a. c. And d. c. Apodized by both changes. Auxiliary structures for temperature compensation are accurately arranged in the coupler device.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to devices utilizing lightwave propagation systems and electro-optical devices, and more particularly, to grating-based devices that perform filtering, combining and other functions.
-assited devices).

BACKGROUND OF THE INVENTION [0002] This application claims the title of the invention as "wavelength-selective optical coupler" on August 29, 1995.
No. 08 / 703,357, filed on Oct. 27, 1995, filed on Oct. 27, 1995, with the title of the invention as "wavelength type optical device". U.S. Provisional Patent Application No. 60 / 055,157, filed on August 4, 1997, entitled "Production of Add / Drop Filter for Wavelength Division Multiplexing" All of these applications are hereby incorporated by reference as if they were made with the national priority of the issue.

[0003] Current communication systems increasingly utilize optical waveguides (optical fibers).
Utilizing the high speed, low attenuation and wide bandwidth characteristics of optical waveguides, data, video signals,
Audio signals can be transmitted simultaneously. An important extension of these communication systems is the use of wavelength division multiplexing, which divides a certain wavelength band into individual wavelengths so that multiplex transmission and reception can be performed with one installation line. This application requires multiplexers and demultiplexers that can divide the band into multiple, but separate, wavelengths that are close to each other (eg, 4, 8, or 16 different wavelengths).
In order to add individual wavelengths to a wide band signal and to extract a certain wavelength from a multi-wavelength signal, a wavelength selective coupler is required, and therefore many add / drop filters are used.
(add / drop filter), a common terminology currently used for this type of device, is evolving.

Because wavelength selectivity is inherent in Bragg gratings, those skilled in the art have devised grating-based devices that add or extract a constant wavelength for multi-wavelength signals. In a typical optical fiber, a light wave is propagated by utilizing a light confinement characteristic and a light guide characteristic of a central core and a low refractive index cladding surrounding the central core. Although wave energy propagates primarily through the core, many add / drop filters or couplers have been developed that use Bragg gratings in one core region of a pair of closely adjacent or contacting parallel fibers. The coupling region is where signals propagating in one fiber are coupled to the other fiber as an essential function of the structure,
Usually referred to as the "evanescent". Wavelength selectivity is provided by an embedded grating that transmits selected wavelengths forward or backward depending on the selected grating characteristics. However, in modern communication systems, this approach has many functional and operational limitations, with factors such as spectral selectivity, S / N ratio, grating durability, temperature stability and polarization sensitivity. Involved.

[0005] The applications described above are based on new theoretical concepts and practical implementations. A narrow body of two fused different fibers is formed between a pair of tapered joints joining at each end. At the barrel, the coalesced fiber is formed by drawing a common commercial size optical fiber precursor, and the diameter is so small that the central core has virtually disappeared. Wave energy is transmitted through the merging fiber regions in two spatially overlapping orthogonal modes. Because the energy of the mode overlap is propagating, the coupling is potentially non-extinguishing in the face of coupling mechanisms such as diffraction gratings. For example, only the selected wavelength of the input signal at the input port is transferred to the drop port by the reflection grating written on the body, while all other wavelengths are reflected to the throughput port. Without propagating through the torso. This reflective grating couples light between the two optical modes in a non-extinguishing manner. Although many advantages are derived from this idea and composition, the realization of all possibilities depends on other developmental factors.

[0006] For example, in current applications, add / drop filters based on this concept provide a powerful grating that can be selectively and accurately set or tuned to a particular wavelength and that has a limited bandwidth. In essence, it needs to be very effective in the shipping channel, be temperature insensitive, compact, low cost, and be immune to apparent reflections or noise in the selected wavelength width. It is also particularly important that the drop efficiency is high and the polarization dependence is small. Further innovations are needed to meet these operational characteristics, while at the same time allowing the repeated production of very small size and sensitive devices.

(Disclosure of the Invention) According to the present invention, the optical characteristics and performance of an asymmetric fusion coupler utilizing a grating are as follows:
It is highly dependent on the physical properties of the body of the coupler. For example, by shaping the shape during stretching or by applying a permanent twist to the body of the coupler after exposing the grating, a polarization independent of the drop wavelength can be achieved. In addition, in the case of a small diameter body, the diameter of the coupler becomes non-uniform due to the fineness of the coupler, but this change in size is compensated for by trimming with a laser or by impressing a refractive index compensation type grating. It turns out that you can. Furthermore, the performance of the grating can be dramatically enhanced by in-diffusing the photosensitive gas during the grating writing process. To improve the spectral properties, the grating comprises a modulated (ac) intensity UV beam and a constant (dc) intensity UV beam.
By simultaneously writing with the beam, it is apolized and ununchired. By choosing the size and other properties of the torso region, the drop wavelength of the coupler is well separated from the back-reflected wavelength, with subsequent wavelengths located outside the frequency band of interest.

[0008] A microcoupler having these characteristics and also the tunability of the wavelength is housed in a prepackaged structure that allows optical access to the coupler body for grid writing. The temperature dependence of the drop wavelength is determined by the stretched structures made of materials having different coefficients of thermal expansion. Furthermore, the drop wavelength is finely tuned by fine-tuning its structure and subsequently maintained over the required temperature range.

The optical fiber type wavelength router according to the present invention is a wavelength selection type filter which is usually called here as an add / drop filter. With such a device utilizing multiple channels at different wavelengths, the selected wavelength channel is directed to the first optical fiber with low loss and high efficiency, while simultaneously transmitting the remainder of the wavelength channel to the second optical fiber. . For example, the above concepts can be used in other applications such as switches, multi-channel routers, cross-connectors, etc., but when applied to add / drop filters, multiplexers and demultiplexers in wavelength division multiplexing (WDM) systems. The maximum profit will be brought directly.

FIG. 1 shows the physical structure of the device. The fusion type coupler is the first fiber 3
1 and 35 and second fibers 30 and 40, the coupling regions 12 of which are different from each other, and the refractive index grating 27 is imprinted. The two fibers may be heterogeneous by tapering one locally by 20% around the fusion zone. Light initiated from the single mode core of the upper fiber 31 is adiabatically emitted in the LP ₁₁ mode with a nominal propagation vector β ₁ at the body and returns adiabatically from the single mode core of the output fiber 35. The light started from a single-mode core of the lower fiber 30, is released just slightly propagation vector beta ₂ the accompanying LP ₀₁ mode in the cross-sectional thermally in barrel, back from the single-mode core of the output fiber 34 to the adiabatic come. When the refractive index grating 27 is engraved on the body of the coupler, or when the wavelengths of β ₁ and β ₂ that satisfy the following Bragg's rule for reflection from the grating period value Λ _g at a specific wavelength of λ _i are selected In

(Equation 1)

The light energy at the wavelength λ _i in the single mode core of the first fiber 31 is continuously reflected (non-evaded) by the grating in the single mode core of the second fiber 30.
nescently). The spectral responsiveness and efficiency of this reflection and mode change coupling process is determined by the continuous coupling strength of the optical mode with the grating. Input mode wavelength

(Equation 2) When detuned to λ _j so that the Bragg rule is no longer satisfied, the input mode in the first fiber 31 propagates through the body of the coupler and the leakage into the second fiber 34 is minimized. Is reproduced as the output mode of the first fiber. For these wavelengths the coupler is transparent, i.e. no coupling occurs and the two fused fibers remain optically independent. Therefore, the light is coupled outside the first fibers 31 and 35 only at the specific wavelength λ _i determined by the grating period in the coupling region 12.

[0012] In addition to back coupling of light to adjacent fibers, the grating typically has the form ₁ (Λ_Two) | = K_gAnd 2 | β_Two(Λ_Three) | = K_gAt some other wavelength obtained from
Light is reflected back to the original fiber. λ_TwoAnd λ_ThreeAre outside the target operating range.
To be β₁And β_TwoThe difference between is large enough. Do waveguides coalesce strongly?
Or the difference increases as the size of the fused coupler body decreases
. Such a general tendency is shown in FIG.
The vertical axis separation between adjacent characteristic curves for smaller diameters (less than V)
Also small) and generally increase. This difference is the difference between L and L for the air-glass optical waveguide.
P₀₁And LP₁₁Β substantially corresponding to the mode₁And β_TwoWith the small body of the coupler
High value. As shown in FIG.₀₁The mode is HE₁₁ ^e, HE₁₁ ^oMo
Is the same expression as LP₁₁The mode is HE_{twenty one} ^e, HE_{twenty one} ^oAnd EH₀₁ ^oThis is a common expression with mode. They do not exhibit periodic symmetry, such as the body of a coupler.
In terms of these LP modes in different waveguide structures, they are technically common.

Furthermore, next to select the inclination angle of the asymmetric grating, the LP ₀₁ mode LP ₀₁ mode, and can reduce the bond strength at the back reflection into LP ₁₁ mode LP ₁₁ mode. Other consideration in inclination of the selection, from LP ₀₁ mode to the LP ₁₁ mode, also is to maximize the efficiency of the mode conversion to the LP ₀₁ mode from the LP ₁₁ mode. A typical angle that minimizes back reflection coupling is 3-5 °, but increases as the diameter of the coupler body decreases. This angle is slightly different from the angle that maximizes drop efficiency.

To construct this optical fiber coupler, two partially different fibers are typically used.
Specifically, fusion is performed so that a narrow body portion having a diameter of 1 to 50 μm is formed, and the fused region is formed.
Waveguides corresponding to at least two supermodes or eigenmodes of the composite waveguide
Form a road. The number of supermodes supported by the composite waveguide structure is
Determined by the refractive index profile and dimensions. In this waveguide structure, the diameter
In the case of a dramatic reduction, the light guiding properties resemble those of an air-glass waveguide. This
Of mode propagation in a simplified step index waveguide
Is partially represented by the V number, which decreases as the radius of the waveguide core decreases, and the wavelength λ ₀ , Core index n_coreAnd cladding index n_cladDepends on. That is,

(Equation 3)

For an air-glass waveguide, n _core = 1.45 and n _clad = 1.0.
For waveguide elliptical cross-section, first-order or low-order mode is nominally LP _01, the second
Mode is nominally LP _11. Typically, the total number of modes supported by such a waveguide is

(Equation 4) And where N is 8-9 in the 1550 nm and 4 μm diameter barrel, higher order modes exist in the coupler barrel. However, the two lowest dimensional modes are essentially important in add / drop operations. Generally, loss peaks appear in any of two or more higher-dimensional modes. Because the two waveguides are sufficiently different and the tapered transition region is long enough, the input optical mode traveling along the single mode core of the original fiber is emitted adiabatically to the supermode of the coupling region . When the coupling region is excited, the supermode is emitted adiabatically back to the original optical mode because it is separated by the waveguide into the two original fibers. There, light energy passes unimpeded from input to output. In a typical asymmetric fiber, (| β ₁ | − | β ₂ |) / (| β ₁ | + | β ₂ |
) = 0.005, and a taper angle of 0.01 radians will result in less than 1% unwanted light energy leakage from one fiber to another. For asymmetry, the same pair of fibers can be made different by leaving one fiber fully stretched (adiabatic pre-tapered) in the central region. The two fibers coalesce or are connected in a coupling region with one waveguide, but the two fibers behave as if they are optically independent. A grating is then cut into the coupling area to transfer light of a particular wavelength from one fiber to the other. For example, a 125 μm diameter fiber may be tapered by 25%, then drawn and fused with another 125 μm diameter fiber to have a taper length of 2 cm, a diameter of 4.5 μm, and a length of 2 cm. Of the body. The resulting taper angle is sufficient to provide a low loss, adiabatic taper. If the period of the grating written by UV is 0.540 μm, the wavelength of the drop channel in the example device is in the 1550 nm range.

The fiber as a suitable starting material that constitutes the coupler may be at least partially clad with a photosensitive material while maintaining the light guiding properties (ie, NA) of a standard single mode core fiber. It is desirable to be characterized to some extent by a light-sensitive cladding that can be manufactured using conventionally known manufacturing methods by diffusing into regions. The purpose of the deposition process used in the present invention is to dope to the critical cladding volume ratio. The more the doping impurities (eg, Ge) are spread along the radial direction of the fiber, the more the resulting body of the coupler becomes more photosensitive after the fusion and stretching steps. It is also important that the fiber be doped with minimal thermal stress and with minimal material mismatch in the doped cladding layer.

A WDM system allows multiple wideband signals to be transmitted over one optical fiber, provided that the individual wavelengths are precisely tuned to predetermined values and that the high S / N ratio is narrow. Must have bandwidth. These properties should be obtained by an add / drop filter, and the invention disclosed or claimed in the above-mentioned application is particularly advantageous in these respects. However, technical requirements have reached the limits as detailed below, and it is not necessary to arrange, test, and burn equipment at each stage, and to produce large numbers of units at low cost. Has a serious problem.

As described in the above-cited application and shown in FIG. 1, an add / drop filter, referred to as a coupler 10, comprises a narrow body 12 formed by an extension from an optical fiber precursor. have. The body 12 is 2-3 cm long and consists of two partially different fibers 14, 15 merged in the longitudinal direction, typically forming a merged region with a cross-sectional dimension of less than 10 μm. Particularly in this example, the trunk 12 is
It has a cross section of a dumbbell-ellipse composite shape, and the dimension (A) in the long axis direction is 10 μm.
Below, the dimension (B) in the minor axis direction is such that the ratio of the major axis to the minor axis is 0.82. The dumbbell-ellipse composite shape (FIG. 2) resembles a cross-sectional shape where the dumbbell shape and the elliptical shape cross each other. In addition, this shape has a laterally asymmetric shape that is most characteristic as a “peanut” or “western shape” shape. The asymmetry is provided by the initial pretaper. The fine fiber 15 in the body 12 is
The relative dimensions can vary by more than 10-30%, but have been stretched and stretched before stretching and coalescing, thereby reducing by about 20% (in this example).
. When the sides of the opposing portions of the fibers 14, 15 are fused and merged, the sides become irregular and oval, preserving the asymmetry of the original fiber. The torso region 12 is preferably stretched without twist, in order to prevent loss of the reference plane, which is here in harmony and merely defines the original core center as a trace. Maintaining this reference plane in the prepackage prior to exposure is important in providing the desired tilt asymmetry on the grid.

At any end of the barrel 12, the fibers are separated by separate tapered coupling branches 20, 21 and 24.
, 25 and a diffusion taper outward over a length of a few cm. This taper is a heat-insulating portion from the small-diameter body portion 12 to a thick single-mode optical fiber (not shown) having a diameter of approximately 90 to 125 μm, and is a transition portion. These fibers are preferably metallized on the outer surface (not shown) to solder the coupler to the prepackage and to maintain accurate and stable tensioning of the coupler after final packaging. . In the body 12, a Bragg grating 27 having a predetermined periodicity suitable for the selected drop wavelength is recorded, and the grating surface is inclined with respect to the larger one of the lateral dimensions of the body 12 ( Usually, 3 ° to 5 °). Multiple wavelengths propagating along one branch, such as the first tapered coupling branch 21, and entering the body 12 are selectively filtered by the Bragg grating 27 so that only the drop wavelength is the second wavelength.
It couples to the tapered coupling branch 20 and to another fiber 30.

According to the present invention, the morphological relationships, dimensions, characteristics, etc. of the couplers are selected, and many advantageous characteristics can be obtained simultaneously if modified. Referring to FIG. 2, the small diameter bodies 14, 15 obtained from the precursor fiber are light sensitive (preferably 8 mol% germanium) in the original cladding region surrounding the thin high index core. Doped, and after stretching there is only a slight fine core of the core.
The energy is then limited and propagated to what is called an air-glass waveguide, where the term "air" means air or some other medium surrounding the actual fiber. Some properties of the air-glass waveguide include multiple apertures and multi-mode waveguide properties. The radial spread of the electromagnetic field out of the fiber is indicated by dotted line 17.

In the body of the air-glass waveguide region (FIG. 2), regardless of whether the light originates at fiber 31 or 30, the orthogonal optical modes are adjacent to fiber 14
, 15 and overlap each other. Due to this perfect mode overlap, if the grid is engraved on the body, the coupling is "non-evanescent" since the modes completely overlap the grid. The optical mode that initially couples to a particular fiber is not localized in the first fiber region in the coupler body. The modes in the torso do not only guide the waves in the original fiber material.

The air-glass waveguide properties of the body of the coupler provide unique optical properties. First,
All lossy cladding modes are eliminated. With a different precursor optical fiber cladding the air interface that can be used as a waveguide, the body of the coupler has a new homogeneous cladding (air), which does not support the second waveguide. The torso supports multiple light modes, but their number is also reduced due to the reduced diameter. However, many high dimensional modes that reduce the short wavelength transmission of the device due to the very small diameter barrel are reduced. These modes are guided to the barrel, and furthermore, they flow out of the fiber into the adiabatic transition region of the tapered section, only providing background loss at certain wavelengths. In addition, due to the suitable tilt asymmetry of the grating, the coupling strength to these higher-dimensional modes can be dramatically reduced or completely suppressed.

FIG. 3 shows the characteristics revealed by analyzing the mode diagram of the body of the elliptical cylindrical coupler. Each curve represents one specific mode supported by one waveguide. Figure 3 shows the literature (Lewis, JE and G. Deshpande
, `` Modes on elliptical cross-section dielectric tube waveguides '', Micr
owaves, Optics, and Acoustics, Vol. 3, 1979, pp. 147-155), and the ellipticity of the coupler is 0.9 (ie, greater than 0.82 which is an example of the present coupler).
Fig. 9 shows a standardized propagation constant for a torso mode. FIG. 3A shows the odd mode, and FIG. 3B shows the even mode. The horizontal axis corresponds to the V number of the waveguide, and the vertical axis corresponds to β / β ₀ = n _eff which formally corresponds to the refractive index of each optical mode in the waveguide.

The waveguide characteristics can also be represented by different mode expressions. For example, LP ₀₁ (Linear polarization) mode is for even and odd HE₁₁Corresponding to a linear combination of modes, L
P₁₁The modes are even and odd EH₀₁Mode and HE_{twenty one}Equivalent to a linear combination of modes
You. The description of the LP mode is useful when analyzing the polarization behavior. Elliptical waveguide
The mode generation characteristics of the road are more familiar with the description of the LP mode.

The slope of these characteristic curves is a constant sensitivity of the effective mode index to the change in diameter. The greater the sensitivity, the greater the leakage and spread of the Bragg grating due to the unevenness of the given diameter. With smaller diameter (lower V number) couplers, the slope is increased and the sensitivity by diameter is also increased. The more challenging uniform diameter requirements of smaller diameter couplers allow for narrower spectral width gratings. In addition, increasing separation between the effective indices of the LP ₀₁ mode and the LP ₁₁ mode, which further separation of large wavelength between dropped wavelength and the backward reflection wavelength (important ones as mentioned below) Corresponding. The gap between these modes and all other high-dimensional modes has also been increased, so that the loss peaks associated with coupling to the high-dimensional modes will cause the loss of spectral regions of interest (eg, 1530-1560 erbium. Make sure to get out of the doped fiber amplifier (EDFA) window.

[0026] Unlike fiber gratings, there is no cladding mode that causes loss in a grating assisted mode coupler, but it is the one that actually coats the coupler material (typically air) that has separate optical This is because it does not have the second waveguide structure supporting the mode. Light propagation is supported only by the body of the doped silica coupler.

The grating-based coupler reflects light from a fiber of a specific wavelength into some fibers (back reflection), and reflects light from a fiber of a different wavelength to other fibers (add / drop). While the add / drop response steers the wavelength required to send light from one fiber to another, the back reflection response is usually undesirable. Thus, the wavelength caused by the back reflection should be outside the operating wavelength range of the add / drop filter. For example, in the 1530-1565 wavelength range for deep WDM applications, the back reflection wavelength is 153
Should be less than 0 nm or greater than 1565 nm or at a wavelength between active wavelength channels. The wavelength separation power of back reflection / drop should be 18nm or more.

This wavelength separation effect can be easily achieved by making the body of the add / drop coupler sufficiently narrow (less than 7 μm), so that the wavelength of the back reflection departs from the wavelength of the drop. By fabricating the fused coupler having a small barrel, the difference between the formal propagation constants of the LP ₀₁ mode and the LP ₁₁ mode is increased. Therefore, the wavelength resolution of the drop and back reflection is also increased. This wavelength separation power exceeds 15 nm for a specially doped original fiber having a main axis of about 3.5 μm and a body having an elliptical cross section. Further, the wavelength separation capability can be further increased by reducing the diameter of the body of the coupler. The exact relationship between barrel diameter and wavelength separation power is strongly dependent on the actual shape and exact refractive index profile of the coupler barrel. Generally, the diameter of the barrel will be less than 5 μm. However, the required uniformity of the torso diameter in the couplers becomes increasingly severe as the torso diameter decreases. Therefore, the wavelength separation of the back reflection / drop is only 15 n if the body diameter is selected normally.
m. A given add / drop filter has a back reflection peak on either the short wavelength side (by the input of the pre-tapered fiber) or the long wavelength side (by the input of the non-pre-tapered fiber) on the side of the drop peak.

For many telecommunications applications in add / drop, such as multiplexer / demultiplexer, the requirement for wavelength separation of this drop / back reflection is substantially the channel spacing of WDM (eg 0.8 nm or (1.6 nm). Therefore, when the wavelength is demultiplexed from the fiber by a sequential method (for example, from the short wavelength side to the long wavelength side), a large resolution is not required. At these wavelengths, those channels have already been pulled out of the fiber by the add / drop filter, even if the longer wavelength device has shorter wavelength back reflections. So, for these units,
The diameter of the barrel may be large, so that the tolerance on the diameter uniformity of the coupler is small.

For most telecommunications applications, the polarization properties of the coupler are important. The light field exists as a vector. It has a direction. This direction is quantified by the polarization state of the light field. The polarization of the optical signal may be linear, circular, elliptical or unpolarized. Two linearly polarized optical signals are orthogonally polarized if the electric field vectors are perpendicular to each other. For example, LP ₀₁ mode and LP ₁₁ modes is substantially x-axis, may be considered along the y-axis are polarized, where the x and y are the major and minor axes of the ellipse.

The input fiber is coupled to the drop filter by a grating type coupler.
The polarization dependent on the wavelength of the light can be immediately represented. This polarization dependence is
This is due to the formation of birefringence in the body of the coupler in the region of the grating. Generally, fusion
The formal propagation constant β of the body of the chosen coupler is the sum of the light in the two orthogonal polarization states.
Not the same. Referring to FIG. 4, this is illustrated by the two dotted peaks.
It can be seen that under these conditions there is wavelength separation between the two orthogonal polarization modes. I
However, the polarization dependence disappears in the cross-sectional shape and refractive index profile of the trunk.
(Ie, | βLP_{01, x}| + | ΒLP_{11, x}| = | ΒLP_{01, y}| + | ΒL
P_{11, y}|). Individually | βLP_{01, x}｜ is ｜ βLP_{01, y}Not equal to |, | βLP _{11, x} ｜ is ｜ βLP_{11, y}Despite not equal to |, the left and right sides of this expression are
Note that they are equal. In practice, contrary to intuition, the torso is a circular cross section of the coupler.
The polarization dependence of the drop wavelength of the part does not disappear,₁₁Mode polarization degeneracy
Does not disappear for a circular waveguide (it is | βLP_{11, x}｜ ≠ ｜ βLP_{11, y}|
), While LP₀₁The polarization dependence of the mode disappears (| βLP_{01, x}|
= | ΒLP_{01, y}|).

One cross-sectional shape of the body where polarization resolution disappears in the drop channel is a composite dumbbell-elliptical shape with a short axis / major axis ratio of 0.8. Another expression includes a "pear" or "peanut" shape. The body cross section is variable in temperature and exposure time to achieve the desired cross section, and is fused by heating performed under a highly controlled and repeatedly heatable heating source until the polarization characteristics disappear. Is stretched under tension. Examples of the heating source include a known heating source, and a CO ₂ (carbon dioxide) gas laser, a gas flame or a resistance heater is preferable. Another torso section is proposed to eliminate polarization dependence, except that a composite dumbbell-elliptical shape was immediately fabricated. It has been demonstrated that the polarization dependence can be reduced to << 0.1 nm by the production of couplers having fairly precise shape asymmetry for the body, preferably an elliptical shape. Current add / drop filters are manufactured by a method that ensures that the polarization separation power of the add / drop wavelength is less than 0.05 nm. The operation of the device is substantially polarization insensitive due to the grating having a FWHM bandwidth of several times the polarization separation power, or about 0.2 nm. Thus, the propagating light spectrum is independent of the polarization of the input signal. As shown in FIG. 5, under that condition the orthogonal polarization modes coalesce with a single drop wavelength.

In another case, if the polarization dependence of the fused coupler remains, dramatically twisting the fused coupler body in the region containing the grating, as shown in FIG. Can be reduced. In other cases, at the desired writing conditions of the UV grating (eg, polarization and intensity), the polarization dependence can be eliminated by UV exposure. A birefringent substance is generated in the glass by the UV exposure treatment, and the birefringent substance can compensate for the formation of birefringence in the body of the coupler.

If the diameter of the body is not uniform, the response of the reflection grating in the body of the coupler often causes undesirable “chirp” or spectral distortion. Is due to the local propagation constant and drop wavelength changing where the diameter changes. Thus, the period of the grating on the non-uniform body will have a wider spectral width than the grating on the uniform body. A grating having a spectral width of 1 Angstroms requires that the change in diameter be less than 0.01 μm in the body of the coupler, which covers the region of the body containing the grating and has a cross section of 5 μm.
Similarly, the coupler geometry should provide a constant coverage of the area containing the grating to prevent leakage and polarization dependence. A highly uniform heating source, such as a reciprocating CO ₂ laser or flame, can provide a highly uniform coupler body. Alternatively, leakage of the response of the grating due to small changes in the diameter of the body portion of the coupler, either by correcting the diameter variation by the local CO ₂ laser heating, engraved on the coupler body part Either by locally varying the grating period to maintain a constant Bragg wavelength, or d. Of background along the grating. c. The refractive index can be substantially reduced or effectively eliminated by the present invention, such as by laser trimming. As shown in FIG. 6, these techniques can effectively reduce spatial variations in the local Bragg wavelength of the grating along the body of the coupler.
This faces a key issue in the production of narrow bandwidth add / drop devices required for 100 and 50 GHz WDM based on grating based couplers. Scanning electron microscopy, atomic force microscopy, by restoring an exponential profile from a complex reflectance profile, or by induced local UV to determine the diameter non-uniformity in a way that can scale up to the manufacturing process
By measuring the fluorescence dose, examining the dependence of reflectivity on position and wavelength, or analyzing the spectral and spatial properties of light scattered across the body of the coupler Can be measured directly.

In addition to forming a uniform grating in the fused coupler, a precisely apodized grating is used to reduce grating sidelobes and eliminate cross-talk between adjacent channels. is necessary. The apodized grating is W
It is important for matching with the required performance of the DM system. It is known that apodization can be achieved by various methods including variable speed scanning, dithering of phase masks and apodized phase masks.

The apodized grating has a modulation amplitude or refractive index a. c. Written by spatially varying the components. However, at the same time, to avoid unwanted leakage or spreading of the grid, d. c. The refractive index or background index must remain very uniform (fluctuations less than 0.0001). Raised cosine (cos ² (z)), sinc ² (z)
, And Gaussian (exp-z ² / 2σ ² ) apodization functions are all effective in reducing the grating sidelobes to -30 dB or less.

The apodized grating exhibits a longitudinal periodic variation of the modulation amplitude of the refractive index as well as a uniform periodic pattern along the waveguide. The grating turns on (turns on) and turns off (over the grating period> 1000) along the direction of light propagation. This smooth variation window function allows spectral ringing and sidebands as a result from a grid with a rectangular window function in shape.
bands). In general, the frequency spectrum of a filter is a Fourier transform of the spatial window function of the filter. An excellent way to achieve apodization is to use exposure scanning, where the contrast of the light interference pattern fluctuates as if the grating were recorded while the total incident intensity was in contrast. To achieve this, the torso region has a counter-propagating d
. c. Beam and modulated a. c. Exposure to the beam and at the same time. The sum of the interference pattern and the intensity of the uniform beam is kept constant, thus eliminating unwanted leakage resulting from variations in the refractive index background. Looking at FIG.
For a cos ² apodized grating, the index function is the apodized periodic wave varying in the form of a bipolar center line over the entire grating length L and obtained below.

(Equation 5)

A. c. The beam intensity is

(Equation 6)

Further, d. c. The beam intensity is given by the following equation.

(Equation 7)

An important advantage of the present invention is that FIG. 7 to FIG.
0 to the features included in the embodiment. The add / drop coupler device 50 comprises a cylindrical housing 52 of stainless steel tubing, which has an outer diameter (OD) of 0.
. 270 "long and 3.67" long, the interior of housing 52 may be referred to as a "prepackage" or support structure 54. The pre-package structure 54 includes the housing 5
The back-to-back assembly inside the 2, but the fiber optic coupler 53 is used as a spare holder to hold accurately throughout the processing steps where the grating is recorded and adjusted. The prepackage structure 54 extends along the longitudinal direction of the housing 52, and the center support member and the retainer of the optical fiber coupler 53 are located substantially along the central axis.

As a first assembly, the opposite end of the fiber optic coupler 50 is a pair of parallel Invar rods 62, 6 extending along most of the length of the housing 52.
3 are fixed to brass end hubs 58, 59 spaced apart above. For soldering and release from impurities, hubs 58, 59 and rods 62, 63 are
Nickel-plated, preferably by a process of electroless metal deposition, they are another element within housing 52.

The prepackaged structure includes an intervening member between the end hubs 58, 59 of a pair of spaced apart base hubs 66, 67, one of which is closest to the end hub 59, Soldered or welded to 1 Invar rod 62. Another base hub 66 is on the second rod 63 and is on the side of the first end hub 58 and adjacent to the reference hub 69 on the second rod.

In the prepackage assembly and phase adjustment, there are rods and hubs that can slide in the longitudinal direction in conjunction with each other. One of the parts comprises a first Invar rod 62, a first end hub 58 and a second base hub 67, all of which are fixed in position on the rod 62. Another assembly is the second Invar rod 63
, A reference hub 69, a first base hub 66 and a second end hub 59. Engaging in this manner, the entire assembly is a jig or tray (shown) containing the torso area of the optical coupler 53 that is open to the optical system placed laterally to write the Bragg grating. ).

The optical fiber in the coupler 53 branches off from the barrel region at each end which is a fusion splice to a standard sized metallized optical fiber. Overall optical coupler 53
Extend near the central axis of the housing 52, thereby providing a hub 58.
, 59, 66, 67 and 69 all pass through a radial slot 70. When the prepackaged structure 54 is fixedly held in a tray in place, the coupler 53 can have end hubs 58 spaced apart in the end region,
It can be soldered to the central area of 59. The torso region is stably configured for light sensitivity and a grid writing step.

If a grating is written in the body region with the selected periodicity, the drop wavelength must be adjusted with sub-nanometer accuracy, substantially minus the temperature range for normal operation. The drop wavelength should be constant between 35 ° C and 85 ° C. Invar alloys have only a very small temperature coefficient, but by themselves do not satisfy athermal. What is needed for the prepackage is to reduce the spacing between the end hubs 58, 59 as the temperature increases. This reduces the tension, so that the strain ε in the coupler body with increasing temperature T satisfies the following equation:

(Equation 8)

In the Ge-doped silica glass, the main contribution of the temperature dependence appears in the first term on the right side of the above equation. It is the temperature dependence of the effective refractive index n _eff . The second term on the right-hand side is the contribution of thermal expansion to the change in the lattice period, and typically has a smaller order than the first term.

Base hubs 66, 67 each have a longitudinally aligned groove 72 around its periphery,
73 and that the adjustment screw 75 extends through the reference hub 69 and the first base hub 66. Thus, after first adjusting the end hubs 58, 59 to match the grid, the stainless steel rod is
, 67, the wavelength is fixed by soldering into the grooves 72, 73. The internal structure within the prepackage determines the internal length, which is not spatially fixed except through the internal stainless steel connection, but is installed at each end It has a different coefficient of thermal expansion from the Invar rods 62 and 63. Each of the base hubs 66, 67 is connected to a different Invar rod 62, 63, respectively, but the end hubs 58, 5, which determine the periodicity of the grid.
From 9 there is a different spacing along each rod.

With the stainless steel rod 80 in place, the unit is inserted into a temperature controlled chamber while reading the drop wavelength by means of optical spectrum analysis.
Cycled through the required temperature range. The adjustment screw 75 extends inward or outward with respect to the reference hub 69 so that the adjustment of the drop wavelength is the same at 25 ° C. as at 85 ° C. In the preferred embodiment shown in FIG.
The adjustment screw has a short thread 76 that meshes with the reference hub 69 and a second thread 77 at the end that meshes with the first base hub 66. As the screw 75 is turned with the screw head 78, the point of engagement of the screw with the reference hub 69 moves longitudinally, increasing or decreasing the length of one Invar section, thereby increasing or decreasing the stainless steel section.

When the prepackage structure 54 including the optical coupler 53 is adjusted, it is moved from the holder or the tray and inserted into the cylindrical housing 52. The prepackage 54 is provided with the second end hub 5 by pleating the housing 52 (FIG. 7).
9 in a position relative to the housing 52. End caps 82, 83 with center holes open for the fibers are fitted to the open ends of the housing 52 and soldered or welded in place. The fibers extending outward from the exit point are soldered in end cages 82, 83 for hermetic sealing. To extend the life of the device, it is desirable to fill the housing 52 with an inert gas before sealing. The outwardly extending fibers are protected from entanglement and distortion by the preferred lengths of retractable tubes 87,88.

The coupler should be hermetically packaged to reduce the propagation of cracks in the body of the coupler after packaging and the breakage of the coupler. If water is present in the package, the coupler is likely to be damaged. This problem is exacerbated when the coupler is packaged under tension, which occurs, for example, when it is necessary to provide a temperature-independent platform. Coupler, argon, helium, nitrogen gas or a mixed gas thereof,
Or, it is desirable to be packaged in any of the group consisting of vacuum.

[0051] Similarly packaged devices can be adjusted by adding an active adjustment mechanism. Applicants disclose in US patent application Ser. No. 08 / 703,357 a low-loss, all-fiber optical switch using two add / drop filters with coupled add and drop ports. . If the drop wavelengths of the two filters match, light from the first fiber will be sent to the second fiber. If the two drop peaks no longer match because one drop wavelength of the filter is de-tuned, the light returns to the first fiber. Thus, an optical signal can be exchanged from one fiber to another. One mechanism for instantly unadjusting the add / drop filter is to irradiate the coupler body with a high intensity exchange beam.
If the beam is of sufficiently high intensity, the refractive index of the barrel changes almost instantaneously (in units of femtoseconds ( ^10-15 seconds)) due to the Kerr effect. By modulating the exchange beam, light can be rapidly exchanged from one fiber to another. This technique does not require precise control over the intensity of the exchange beam. It's just
It only needs to be strong enough to make the two filters untuned. Silica glass used in the production of optical fibers does not exhibit large optical nonlinearity, and therefore requires relatively high optical strength. However, other optical materials, such as specially doped silica, electrically polarized silica, crystalline or polymeric materials, are promising candidates for this application. Another mechanism for converting the add / drop filter is to surround the coupler body with a gas, liquid, or other material whose optical properties are controlled by electrical, magnetic, and optical control signals. It can be changed by addition. An example is a liquid crystal, the refractive index of which changes with the application of an electric field.

[Brief description of the drawings]

FIG. 1 is a simplified and idealized view of the main part of the invention, namely the tapered coupling branch and body region of a coupler according to the invention, which is useful in describing the modes and characteristics of an optical waveguide.

FIG. 2 is an enlarged cross-sectional view of the asymmetric body of the coupler in FIG. 1, showing the magnitude of light wave energy propagating along the waveguide shown by the dotted line.

FIG. 3 (A) how lossy cladding modes are eliminated, how a suitable separation between the decreasing wavelength and the wavelength of back reflection is achieved, and how the diameter is reduced. Showing the relationship between the standardized propagation constant and the V-number for the waveguide employed in these devices, which is useful in understanding whether the uniformity tolerance of the device is related to the diameter of the coupler ( Odd mode) graph.

FIG. 3 (B) is a graph (even mode) similar to FIG. 3 (A).

FIG. 4 is a simplified and idealized view of a coupler twisted in the torso region transmitting polarization independence.

FIG. 5 is a schematic diagram illustrating a decrease in reflectivity with respect to wavelength, illustrating a torsional effect on the drop channel spectral characteristics, ie, the polarization separation characteristics of the decreasing channel.

FIG. 6 (A) shows the change in local Bragg wavelength along a typical non-uniform diameter coupler before correction.

FIG. 6B is a diagram showing a change in a local Bragg wavelength after correction.

FIG. 7A shows UV-induced refractive index changes in couplers with apodized gratings, such as cosine square function or Gaussian apodization function (unscaled).

FIG. 7 (B) is a diagram similar to FIG. 7 (A).

FIG. 8 is a cutaway perspective view of an exemplary coupler of the present invention having a cylindrical housing and an optical fiber support structure or prepackage.

FIG. 9 is a side sectional view of the coupler of FIG. 8;

FIG. 10 is a partial side sectional view of a fine adjustment mechanism for wavelength compensation in the couplers of FIGS. 8 and 9;

FIG. 11 is a partial cross-sectional side view of the distal end of the coupler showing how the housing of the coupler is hermetically sealed and the fibers inside are protected.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Add / drop filter 12 Coupling area | region (body part area | region) 14, 15 Small diameter body part (fiber) 20, 21, 24, 25 Taper connection branch 27 Bragg grating (refractive index grating) 31, 35 1st fiber 30, 40 Second fiber

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] February 4, 2000 (200.2.4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM, HU, ID, IL, IS, JP, KE, KG, KP, KR , KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZW. (72) Inventor Shaolin Tong, United States 91106 Pasadena, California, South Wilson Avenue 241; Apartment 101 56th F term (reference) 2H037 BA31 CA07 CA33 CA35 DA04 DA06 DA12 DA17 DA36 2H047 KA01 KA13 KB06 LA03 LA19 MA01 MA05 PA00 PA22 QA07

Claims (1)

Claims 1. A different optical mode independently propagates except for a specific wavelength at which at least one forward propagating optical mode may couple with at least one backward propagating optical mode. A multi-mode light propagating element comprising a light confinement region defined by substantially optically independent coalescing optical fibers arranged to operate. 2. The element according to claim 1, wherein the optical fibers are adjacent to each other in the longitudinal direction in the united region and have different cross sections at the side portions of the optical fiber. 3. The device according to claim 1, wherein the optical fibers are united along a longitudinal direction, and optical modes propagating in a forward direction and a backward direction are orthogonal to each other. Wherein the shape of the united area, with Although modal birefringence of LP ₀₁ mode and the LP ₁₁ mode match is deformed to the opposite direction, dropped wavelength is polarization insensitive 4. The device according to claim 3, wherein the device comprises: 5. The device according to claim 1, wherein the difference in propagation constant for the orthogonal polarization component of the optical mode is substantially eliminated, and the specific wavelength of the device is substantially independent of polarization. 4. The device according to claim 3, wherein the device is twisted about a direction. 6. The combination of claim 1 wherein the coalescing region has a diameter and a refractive index such that energy propagates along the fiber body as well as the periphery surrounding the fiber body. Element. 7. The fiber, wherein the original core is traced,
2. The device of claim 1, wherein the original cladding is an extended cladding optical fiber substantially occupying a majority of the fiber. 8. The device of claim 7, wherein the fiber has a diameter of less than 10 μm and is selected to minimize the number of high-dimensional modes that cause loss in a range of operating wavelengths of interest. 9. The united fiber region generally has a short axis / long axis ratio of about 0.5.
9. The device of claim 8, wherein the device has a dumbbell-elliptical cross-section. 10. The device of claim 7, wherein at least one original cladding in the fiber comprises a diffraction grating. 11. The element includes a tapered optical coupling branch that adiabatically transitions from the coalescing region to the optical fiber, and a diffraction grating that reflects energy of a selected wavelength between the optical fibers. The device according to claim 10. 12. The element of claim 11, wherein the element includes a body region in which the fibers are fused together in a longitudinal direction and the lattice plane is inclined at an acute angle in a direction perpendicular to the direction of propagation. An element as described. 13. The device according to claim 10, wherein a displacement of a propagation constant along a longitudinal direction of the diffraction grating is locally compensated in the body region. 14. The method according to claim 13, wherein said compensation is performed by a laser.
An element according to claim 1. 15. The device according to claim 10, wherein the diffraction grating is apodized in a longitudinal direction. 16. The apodization function comprises a refractive index variable about a center line, and a. c. Components and d. c. 16. The device of claim 15, wherein the component contains both components. 17. If L is a lattice length and z = 0 is the center of the length of the lattice, a. c. The envelope function of the component varies substantially according to Δncos ² (π / Lz) (sink _g z + 1), and d. c. Component device according to claim 15 consisting of changing substantially in accordance with -Δncos ² (π / Lz). 18. The element of claim 1, wherein the adjacent fibers are fused together to form a coupler element along a length and include a diffraction grating at the length. . 19. The device of claim 10, wherein said diffraction grating reflects both a drop wavelength and a back-reflected wavelength, and wherein said device comprises means for causing separation between said drop wavelengths. . 20. The device of claim 19, wherein the fiber in the region of the diffraction grating is sufficiently small in cross-section that the back reflection wavelength shifts outside the operating wavelength range of the device. 21. A support comprising at least one rigid unit coupled to plug one of the longitudinal ends of said element through which light propagates into a selected space, said rigid unit comprising a selective unit. The device of claim 10, further comprising a temperature compensator for adjusting an adjacent interstitial space between the ends of the device over a defined temperature range. 22. The device according to claim 21, wherein the support is arranged to allow light access to the grating region of the fiber. 23. A housing means for enclosing the support and the optical fiber and including a hermetic seal for insulating the inside of the housing from the surroundings is further provided, and a protective gas is sealed inside the housing of the housing means. 22. The device according to claim 21. 24. An elongate hollow housing, and an optical waveguide coupler element extending within and along the housing,
The coupler element includes a central narrow body extending along the housing;
An optical waveguide coupler element having two pairs of ends of the optical fiber extending out of the opposite end of the housing; and a support element for the coupler element including at least one area of engagement with the housing. The support element is coupled to the coupler element at an opposite end of the coupler element and has a length and tension that varies over a temperature range and provides spatial access for optical access to the body region. 19. The coupler element according to claim 18, comprising a support element including a support element supporting the coupler body which is separated from each other, and hermetic sealing means for closing both ends of the cylinder. 25. The support element includes a pair of temperature-uniform rods extending substantially along a cylindrical axis, and a pair of end hub elements spaced along the rods at predetermined intervals. A third rod comprising a prepackage, wherein the prepackage further has a different coefficient of thermal expansion than the pair of rods and is specifically coupled to the pair of rods to compensate for temperature changes. 25. The coupler of claim 24, comprising: 26. A pre-package comprising: a pair of internal hub elements that engage different regions of a third rod mechanism at predetermined intervals with different ones of the pair of rods; and one of the internal hub elements for adjusting a temperature range. 26. The coupler of claim 25, comprising: 27. The coupler according to claim 26, wherein the coupler comprises a metallized coupler element soldered to end hubs at both ends of the body region, and a protective atmosphere is enclosed inside the housing. The coupler according to 1. 28. The body region of the coupler having a diameter of less than 10 μm,
28. The housing of claim 27, wherein the housing is cylindrical with a diameter of less than about 5 mm, and wherein the coupler comprises means provided near an end of the housing to limit bending of the end extending from the fiber. Coupler. 29. The coupler element according to claim 28, wherein the coupler element includes a diffraction grating in a narrow body, and the end hub supports the coupler element under tension.
The coupler according to 1. 30. The coupler according to claim 29, wherein the tension is a value suitable for maintaining the elongation of the coupler body between 0.1% and 0.5%. 31. The pair of rods is made of Invar, the third rod is made of stainless steel, and the adjustable mechanism is a fifth rod that moves along an Invar rod adjacent one of the inner hubs. 31. The coupler of claim 30, comprising a hub, a threaded element passing through the fifth hub, and an adjacent internal hub. 32. The torso region is in the range of about 2-3cm in length, and each pair of ends of the optical fiber is in the range of about 2-3cm in length, and the torso region is Composite dumbbell of fused fiber having a cross-sectional size in the range of 3-6 μm
32. The coupler of claim 31, comprising an elliptical cross section, wherein one fiber comprises about 15-25% thinner than the other fiber. 33. The hub having a circular perimeter located within a cylinder, wherein an Invar rod extending through the hub is located on a common plane, and
33. The coupler of claim 32, wherein the two inner hubs have longitudinal circumferential alignment grooves and the stainless steel rods are mated and secured with the circumferential grooves. 34. An optical fiber coupler including a Bragg grating for outputting an output of a selected add / drop wavelength in response to an input signal in a target band wavelength, the optical fiber coupler having a body region where two fibers are combined. And including a Bragg grating extending along a longitudinal axis of the fiber coupler and a pair of bifurcated arms extending substantially along the longitudinal axis from each end of the torso region. A fiber optic coupler, supporting the forked arms and securing them at their isolated ends to provide tension in the torso region to equalize the periodicity of the Bragg grating over a selected temperature range. A coupler carrier element provided with a mechanism for stabilizing the tension applied to the trunk region, and a hermetically sealed enclosure surrounding the coupler carrier element and the optical fiber coupler. 19. The coupler element according to claim 18, comprising a housing formed. 35. The coupler of claim 25, wherein the coupler operates in a temperature range of 25 ° C. to 85 ° C. within a wavelength band of interest from 1530 nm to 1565 nm, and wherein the carrier element comprises an elongated element having at least two different coefficients of thermal expansion. The elongated element is arranged to compensate for the thermal fluctuation of the optical fiber coupler by adjusting the tension acting on the optical fiber coupler, and comprises an adjusting device for setting a temperature range to be compensated. 35. The coupler of claim 34, wherein the coupler comprises: 36. A photoreceptor having a trunk region having a cross-sectional size of less than 10 μm in the center, the photoreceptor having only a trace core, wherein the photoreceptor comprises a wavelength-selective Bragg grating. A coupler element having two longitudinally fused fibers, wherein the photosensitizer has a geometric cross-section so that the coupler is insensitive to the polarization of light propagating therein. 19. The coupler element according to claim 18, comprising: 37. The central torso region has an elliptical cross-section with a short axis / major axis ratio of 0.8, and the grid is inclined about 3 ° to 5 ° with respect to the longitudinal direction. 37. The torso region device of claim 36. 38. The body region has a local index of refraction d to compensate for changes in cross-sectional size to induce a spectral width of a wavelength selected by a Bragg grating.
. c. The torso region device according to claim 37, comprising a displacement. 39. The cross-section of the fiber is small enough that it cannot support the loss cladding mode and the spread of wavelength separation between the wavelength selected by the Bragg grating and the back-reflected wavelength from the grating. 39. The torso region device of claim 38, further comprising: 40. The method of manufacturing a coupler element according to claim 18, wherein a supporting device supports the coupler device at two locations separated from each other, and an area of the coupler device between the two locations. Writing a grating to the grating; applying a tension to the coupler until the drop wavelength of the grating can respond to the tension; compensating for a temperature change in a predetermined range; and selecting a temperature compensation range. Adjusting the temperature to a predetermined temperature range. 41. The coupler device of claim 40, wherein the coupler device is supported between the two locations, and wherein the grating is written in a central torso region of the coupler device. Production method. 42. The method according to claim 41, wherein the two locations are bonded to a supporting device using a metal solder to couple the optical coupler to the metal substrate. 43. The solder comprises selecting from a metal or metal alloy that maximizes size stability so as to accurately preserve the drop wavelength of the device during operation of the coupler device. 43. The method for manufacturing a coupler element according to 42. 44. The method according to claim 42, wherein the metal solder is substantially made of an indium alloy. 43. The method of claim 42, comprising the step of coating at least a portion of the optical coupler by depositing a metallization layer on the glass material of the coupler such that bonding to the metal solder is achieved. Manufacturing method of coupler element. 44. The method of claim 40, further comprising the step of longitudinally stretching the optical fiber to form a narrow cross-section body abutting the tapered portion in the coupler device prior to the writing step. Of manufacturing a coupler element. 45. The method of claim 44, further comprising the step of forming a body region united with the optical fiber. 46. The method according to claim 45, further comprising the step of pulling one of the fibers to make it thinner than the body region of the other fiber. 47. The method according to claim 47, wherein the one fiber is one more in the body region than the other fiber.
47. The method for manufacturing a coupler device according to claim 46, wherein the coupler device is thinned by 0 to 25%. 48. The method according to claim 40, further comprising diffusing a photosensitive material into the coupler during the writing step. 49. The method according to claim 48, further comprising a step of diffusing a dopant selected from the group including hydrogen or deuterium into the coupler in order to enhance photosensitivity. 50. The method according to claim 44, further comprising the step of controlling the cross-sectional shape of the trunk region during the stretching step. 51. The shape of the body region is shape-controlled to provide polarization independence at the drop wavelength of the device.
3. The method for manufacturing a coupler device according to item 1. 52. The method according to claim 51, wherein the coupler has a cross section of a composite dumbbell-ellipse in a body region. 53. The method according to claim 52, wherein the cross-sectional shape of the composite dumbbell-ellipse has a short axis / long axis ratio of about 0.8. 54. The coupler device of claim 44, further comprising measuring a change in cross-sectional size of the coupler body and writing a refractive index change in the body region for compensation. Manufacturing method. 55. The change in the refractive index is obtained by adding d. c. 55. The method of claim 54, wherein the method is written as a change. 56. The length of the extended optical waveguide is reduced in cross-sectional size to a size that reduces the number of loss modes, thereby reducing the grating drop wavelength to the back reflection wavelength. The method for manufacturing a coupler device according to claim 44, wherein the method comprises shifting. 57. The method of claim 40, wherein the step of tensioning and temperature compensating the coupler comprises using a selected length of differential thermal expansion of different materials to reduce tension with increasing temperature. The manufacturing method of the coupler element of Claim. 58. The method of claim 57, further comprising attaching the coupler having a centrally extending region. 59. The method according to claim 58, further comprising a step of hermetically enclosing the optical coupler and the supporting device. 60. The method according to claim 59, further comprising a step of providing a protective atmosphere to the enclosed space.