Optical module

Abstract

To provide an optical module capable of stably operating by suppressing an increase in optical coupling loss caused by a warp of a fixing member, a package bottom surface, or the like.SOLUTION: In an optical module, a package enclosing an optical device including an optical element is fixed via a flange. The flange includes two connection portions on each of both side surfaces in a parallel direction and an optical axis direction of an optical signal guiding the optical element, and an interval between respective width centers of the two connection portions is configured to be narrower than twice the length in the parallel direction and the optical axis direction of a carrier fixing portion that fixes the optical device inside the package.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an optical module.

Background Art

[0002] In optical communication, for wavelength conversion, optical modulation, optical measurement, or optical processing of optical signals, as well as in various fields such as medicine and biotechnology, development of optical devices (nonlinear optical devices and electro-optic devices) for generating and modulating coherent light over the ultraviolet - visible - infrared - terahertz range has been progressing.

[0003] In addition, various research and developments have also been carried out on nonlinear optical media and electro-optic media used in such optical devices. In particular, oxide-based compounds such as lithium niobate (LiNbO3: hereinafter referred to as LN) have high second-order nonlinear optical constants and electro-optic constants, so there are many research report examples as materials for optical devices, and they are positioned as promising material systems for practical use.

[0004] As an example of an optical device that develops the high nonlinearity of LN, a wavelength conversion element using periodically poled lithium niobate (hereinafter referred to as PPLN) can be cited. The wavelength conversion element using PPLN can perform second harmonic generation (SHG), difference frequency generation (DFG), and sum frequency generation (SFG) using the second-order nonlinear optical effect, and has a high wavelength conversion efficiency, so there have been many research report examples so far.

[0005] In addition, by using a wavelength conversion element having such a high wavelength conversion efficiency, it is also possible to configure an amplifier for signal light, called optical parametric amplification, by transferring energy from the pump light power to the signal light. Furthermore, since the wavelength conversion efficiency is proportional to the power density of the light propagating through the nonlinear medium, it is also possible to obtain high efficiency by forming a waveguide structure and confining the light in a narrow region. For this reason, research and development on wavelength conversion elements having a waveguide structure using a nonlinear medium having a high second-order nonlinear optical constant such as PPLN has been actively carried out. In particular, in recent years, from the viewpoint that the characteristics of the bulk of the crystal can be directly utilized, there are many reported examples of research on wavelength conversion elements having a ridge-type optical waveguide structure having characteristics such as high optical damage resistance, long-term reliability, and easy device design.

[0006] In order to stably operate such an optical device having a high conversion efficiency, module implementation is essential. As an existing module implementation, for example, a module having two optical inputs and two optical outputs has been proposed (for example, Non-Patent Document 1). According to this, it has been reported that the optical parametric gain reaches 20 dB or more.

Prior Art Documents

Non-Patent Documents

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Generally, an optical module is rarely installed and operated alone, but is implemented in a form fixed within a housing. When fixing, if the flatness of the base on which the optical module is fixed, such as a fixing member, is low (for example, warped), a positional displacement of the optical system of the optical module may occur, and accordingly, optical coupling loss may be caused.

[0009] FIG. 1 is a diagram showing the structure of an exemplary optical module 100 according to the prior art, where (a) shows a top view and (b) shows a cross-sectional view taken along the cross-sectional line Ib-Ib. As shown in FIG. 1, the optical module 100 includes a carrier 101, an optical element 102 placed on the carrier 101, internal optical systems 103a and 103b placed on the carrier 101 on each of the input side and the output side with respect to the optical axis direction of the optical element 102, a package 104 that encapsulates these elements, external optical systems 105a and 105b installed on each of the input side and the output side of the signal light that guides the optical element 102 on the side surface of the package 104 in a direction orthogonal to the optical axis direction, optical fibers 106a and 106b connected to each of the external optical systems 105a and 105b, a carrier fixing portion 107 that connects the bottom surface of the carrier 101 and the inner surface of the package 104, a flange 108 connected to the side surface of the package 104, and a fixing member 109 connected to the bottom of the flange 108.

[0010] Furthermore, as shown in FIG. 1, the flange 108 of the optical module 100 is configured such that the length in the direction parallel to the optical axis (the y direction in FIG. 1) is approximately the same as the length of the package 104 in the direction parallel to the optical axis. In addition, the flange 108 has three (six in total on both sides) notches 110a-f arranged at equal intervals on both side surfaces in the direction parallel to the optical axis. On the other hand, screw holes (not shown) are formed in the fixing member 109 at positions corresponding to each of the notches 110a-f. Then, by inserting screws into these screw holes, the package 104 and the elements encapsulated therein (optical element 102, internal optical systems 103a, b, etc.) and the fixing member 109 are configured to be mechanically fastened via the flange 108.

[0011] In the optical module 100 having such a structure, when the fixing member 109 has a warp in the thickness direction (the z direction in FIG. 1), the package 104 and the elements encapsulated therein (optical element 102, internal optical systems 103a, b, etc.) may also have a warp. The occurrence of such warps in the package 104 and the elements may lead to an increase in the optical coupling loss of the signal light guided between the elements, causing a decrease in the transmission efficiency.

[0012] FIG. 2 is a diagram showing the structure of an exemplary optical module 200 according to another example of the prior art, where (a) shows a top view and (b) shows a cross-sectional view taken along the cross-section line IIb-IIb. Different from the above-described optical module 100, the optical module 200 has a form in which the bottom surface outside the package 104 is directly joined to the fixing member 109 instead of being mechanically fastened via the flange 108.

[0013] In the optical module 200 having such a structure, the bending stress generated by the warp of the fixing member 109 mainly occurs in the carrier fixing portion 107. Therefore, the amount of deformation (warp) of the carrier 101 can be suppressed to be small as compared with the case of the optical module 100. However, in the optical module 200, since there is a difference between the warp amount of the package 104 and the warp amount of the carrier 101, an optical axis shift occurs between the internal optical system 103a and the external optical system 105a, and between the internal optical system 103b and the external optical system 105b. As a result, an increase in optical imaging loss may occur.

[0014] Thus, the warp of the base (such as a fixing member) to which the optical module is fixed causes an increase in optical coupling loss. In particular, in an optical module having a free space optical coupling system as shown in FIGS. 1 and 2, the increase in the optical coupling loss becomes remarkable. In the above description, the case where the fixing member is warped has been described. However, in a structure such as the optical module 200, the same problem may occur when the bottom surface of the package 104 has a warp. Further, even if the optical module is not fixed to a fixing member but is not fixed to another base, the same problem may occur if the other base has a warp.

[0015] In addition, the increase in optical coupling loss due to such a warp is not limited to the module of the wavelength conversion element described above, and may occur in the same manner even in the case of an optical module having only an input terminal such as an optical detection module or only an output terminal such as a laser module.

[0016] As an existing technique for suppressing the optical coupling loss caused by the warp in such an optical module, for example, a proposal for package deformation due to thermal stress can be cited. However, in such a technique, when fixed at the diagonal of the package, there is still a problem that it may be affected by the warp of the fixing member.

[0017] As another example of the existing technology, there is a method of arranging two fixed points in a direction orthogonal to the long side of the package. However, in this case, another problem may occur in that the mechanical reliability decreases because the vibration mode frequency with the fixed points as fulcrums becomes low.

[0018] Furthermore, several other solution techniques have been reported, but in these solution techniques, heterogeneous material bonding and notch processing are often required. In such cases, there is a problem that the cost for manufacturing the flange structure increases.

Means for Solving the Problems

[0019] The present invention has been made in view of the above problems, and an object thereof is to provide an optical module that can operate stably by suppressing an increase in optical coupling loss caused by warping of a base (such as a fixing member or the bottom surface of the package) to which the optical module is fixed.

[0020] In order to achieve the above object, the present invention provides an optical module in which a package enclosing an optical device including an optical element and a fixing member are mechanically fastened via a flange, and the flange is provided with two notches on each of both side surfaces in a direction parallel to the optical axis direction of an optical signal that guides the optical element, and the interval between the width centers of each of the two notches is configured to be narrower than twice the length in the direction parallel to the optical axis direction of a carrier fixing portion that fixes the optical device inside the package.

Effects of the Invention

[0021] According to the present invention, it is possible to provide an optical module in which optical coupling loss of signal light caused by warping is suppressed and which can operate with high efficiency and stability.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, various embodiments of the present invention will be described in detail with reference to the drawings. The same or similar reference numerals indicate the same or similar elements, and redundant descriptions may be omitted. The materials and numerical values are for illustrative purposes and are not intended to limit the technical scope of the present disclosure. The following description is an example, and unless departing from the gist of an embodiment of the present invention, some configurations may be omitted, modified, or implemented with additional configurations.

[0024] FIG. 3 is a diagram showing the structure of an optical module 300 according to an embodiment of the present invention, where (a) is a top view, (b) is a cross-sectional view taken along the IIIb-IIIb cross-sectional line, and (c) is a side view in a plane parallel to the xz plane. As shown in FIG. 3, the optical module 300 is an optical module including an optical device of a spatial optical coupling system in which a package 104 and a fixing member 109 are mechanically fastened via a flange 308, similar to the optical module 100 according to the prior art. The flange 308 has two notches 310a-b and 310c-d on each of both side surfaces in the direction parallel to the optical axis direction, and the interval w f (hereinafter, for simplicity, the notch interval w f is referred to as) is configured to be narrower than twice the length w c (hereinafter, for simplicity, the carrier fixing portion width w c is referred to as) in the direction parallel to the optical axis direction of the carrier fixing portion 107 (k to be described later is 0.5 or less).

[0025] In FIG. 3, the carrier 101 is depicted as being placed on the carrier fixing portion 107, but this is for illustration purposes and does not limit the structure of the optical module 300. For example, the carrier 101 may be placed on a Peltier element instead of on the carrier fixing portion 107 (in other words, the carrier fixing portion 107 may be replaced by a Peltier element). Further, the Peltier element may be connected to a thermistor for measuring the temperature of the optical element 102. The flange 308 may be molded as a separate member and joined to the package 104 by welding or the like, or may be molded integrally with the package 104 or a part of the package 104, as long as it protrudes from the package 104. The shape of the notches 310a-b and 310c-d may be a shape into which a screw can be inserted, such as a hole shape, instead of the cutout shape as shown in the figure.

[0026] In the optical module 300 having such a configuration, as described above, the notch interval w f is the carrier fixing portion width w cIt is defined to be narrower than twice this. This notch interval w f is set from the viewpoint of efficiently suppressing optical coupling loss, and this is the greatest feature of the optical module according to the present invention. Below, the basis for setting this notch interval w f will be described in detail.

[0027] FIG. 4 is a diagram showing the result of evaluating the increase in optical coupling loss with respect to the change in the notch interval w f in the optical module 300 by three-dimensional stress-optical simulation. In this simulation, the optical module 300 is assumed to be in a form in which the carrier 101 is placed on the Peltier element. Also, in the optical module 300, the length in the direction parallel to the optical axis direction of the package 104 (y direction in FIG. 3) is assumed to be 66 mm, the length in the direction parallel to the optical axis direction of the carrier 101 is assumed to be 50 mm, and the length in the direction parallel to the optical axis direction of the Peltier element is assumed to be 16 mm.

[0028] Further, in this simulation, the optical element 102 is assumed to be a second-order nonlinear optical element, and its refractive index is assumed to be of the same degree as that of LN. However, this is for illustrative purposes, and the optical element 102 is not necessarily limited to a second-order nonlinear optical element. Furthermore, in this simulation, the optical element 102 is assumed to have a ridge-type waveguide structure, but the optical element 102 does not necessarily need to be a waveguide structure. In addition, in this simulation, the optical device encapsulated in the package 104 is assumed to be a free-space optical coupling system device, but it is not necessarily limited to this, and other forms of devices (for example, a device in which each element is coupled by an optical fiber) may be used.

[0029] For the optically simulated module 300 thus, in this simulation, a curvature radius of 10 m is imparted to the fixing member 109, and in that state, the increase in optical coupling loss with respect to the lengths of various notch intervals w f is calculated. As a result, as shown in FIG. 4, the notch interval w fWhen it becomes 30 mm, the increase in optical imaging loss is most suppressed, and the notch interval w f When it spreads more than that, as the warp of the flange 308 increases, a tendency for the increase in optical coupling loss to increase was recognized. This notch interval w f The value of 30 mm corresponds to approximately twice the length in the direction parallel to the optical axis direction of the Peltier element, that is, w c (16 mm). In addition, when the carrier 101 is placed on the carrier fixing portion 107, the length in the direction parallel to the optical axis direction corresponds to the length in the direction parallel to the optical axis direction of the carrier fixing portion 107.

[0030] Generalizing this behavior, it is explained by the following model.

[0031] FIG. 5 is a diagram showing a model 500 that generalizes the behavior of the occurrence of optical coupling loss due to the warp of the fixing member 109. As shown in FIG. 5, the model 500 is a two-dimensional model corresponding to the side cross section of the optical module 300 shown in FIG. 3, and is an axisymmetric model with the center line of the length in the y direction (direction parallel to the optical axis direction) (shown by a one-dot chain line in FIG. 5) as the axis. And in such a model 500, if the angle formed by the center line and the perpendicular line at the end of the long side of the carrier fixing portion 107 is θ1, the angle formed by the center line and the perpendicular line at the notch width center of the flange is θ2, and the angle formed by the perpendicular line of the center line and the waveguide direction of the signal light passing through the external optical systems 105a and b is θ3, then θ1, θ2, and θ3 are represented by (Equation 1), (Equation 2), and (Equation 3), respectively.

[0032]

Equation

[0033] Here, w c is the carrier fixing portion width, w fThe notch interval is, and R is the radius of curvature of the fixing member 109. Also, k is a coefficient for converting θ2 to θ3.

[0034] Furthermore, the perpendicular to the center line can be regarded as the line corresponding to the optical axis when no warping occurs, that is, the line when the optical axes of the signal lights guiding each of the elements (optical element 102, internal optical systems 103a, b, external optical systems 105a, b) all coincide. Also, in the model 500, the angle formed by the perpendicular to the center line and the guiding direction of the signal light passing through the internal optical systems 103a, b can be regarded as having the same value as θ1 uniquely. This is because the warping amounts of the carrier 101 and the optical element 102 and the internal optical systems 103a, b mounted thereon are limited by the warping amount of the carrier fixing portion 107.

[0035] Here, it is assumed that the overall warping of the package 104 is proportional to the bending stress causing the warping. Then, the angular deviation θ d between the internal and external optical systems of the package 104 is given as the difference between θ3 and θ1, and is expressed by (Equation 4).

[0036]

Equation

[0037] Furthermore, here, considering the optical coupling rate calculation by Gaussian beam approximation, the optical coupling rate η of an optical beam with a width of ω is considered. Then, the optical coupling rate η in the case where the angular deviation is θ -2 is expressed by (Equation 5). d

Equation

[0038]

Equation

[0039] Here, λ is the wavelength.

[0040] And in this (Equation 5), the optical coupling loss is minimized when (Equation 6) holds.

[0041] [Number]

[0042] Here, considering the results in FIG. 4, k is determined to be 0.5. As described above, this is due to the fact that in FIG. 4, the notch interval of 30 mm corresponds to approximately twice the length of the long side (16 mm) of the Peltier element (carrier fixing portion 107).

[0043] When k is 0.5 or less, it corresponds to the case where the notch interval w in FIG. 4 f is 30 mm or less. Therefore, in the optical module 300 set as described above, an increase in optical coupling loss is suppressed to a small extent. On the other hand, when k is greater than 0.5, conversely, in the optical module 300, an increase in optical coupling loss becomes significant, and the transmission efficiency decreases.

[0044] That is, in the optical module 300, when the notch interval w f is designed to be narrower than twice the carrier fixing portion width w c , it can be said that optical coupling loss can be efficiently suppressed. In the optical module 300 according to the present invention, the notch interval w f is designed based on such a concept. Thereby, even when the fixing member 109 is warped, it is possible to provide an optical module capable of suppressing optical coupling loss more efficiently than existing technologies.

[0045] In addition, in the description regarding the above-described model 500, it has been described that the center of the notch interval w f and the center of the carrier fixing portion width w c coincide (corresponding to the above-described axis), but as long as equations (1) to (6) hold, the centers of the two do not necessarily have to coincide. However, the positions of the two notches 310a-b and c-d in the flange 308 are w cWhen it is disposed at a position outside, the optical axis deviation of the external optical system increases, and as a result, the optical coupling loss increases. For this reason, it is preferable that the two notches 310a-b and c-d disposed on each of the both side surfaces of the flange 308 be disposed within the range of the length in the direction parallel to the optical axis direction of the carrier fixing portion 107.

[0046] Also, in the above description, it has been described that the optical element 102 has a refractive index equivalent to that of LN. This means that in the optical module 300 according to the present invention, a material having a refractive index equivalent to that of LN may be applied to the optical element 102. Therefore, in the optical module 300 according to the present invention, the material of the optical element 102 is, for example, LiNbO3, LiTaO3, LiNb (x) Ta (1-x) TaO3 (0≤x≤1), or a material containing at least one selected from the group consisting of Mg, Zn, Sc, and In as an additive thereto, exhibits the same effect. Further, even if the optical element 102 has a periodically poled inversion structure, since the refractive index itself does not change, the same effect is exhibited.

[0047] Generally, in an optical module of a free space optical coupling system, the reduction of the optical coupling loss due to the warpage described above appears more remarkably as the length in the direction parallel to the optical axis direction of the package is longer. Therefore, the optical module according to the present invention exhibits a higher effect particularly when the performance is determined by the length in the direction parallel to the optical axis direction of the package. For example, the optical module according to the present invention can more effectively suppress the optical coupling loss when the optical element is PPLN or silicon photonics.

[0048] In addition, in the above description, it is assumed that the fixing member 109 is warped so as to be convex with respect to the package 104 side. However, conversely, a case where the fixing member 109 is concave with respect to the package 104 side is also conceivable. In such a case, it is possible to compensate by filling the convex portion with a material such as metal to fill the gap in the concave portion.

[0049] In the above description, the optical module 300 has been described as being fixed to the fixing member 109, but this is for illustrative purposes, and the optical module 300 does not necessarily have to be fixed to the fixing member 109. For example, the optical module 300 may be fixed to another base (e.g., a substrate, etc.) via the flange 308.

[0050] Furthermore, the fixing method of the optical module 300 is not limited to mechanical fastening, and other joining methods may be applied. For example, a position corresponding to the notches 310a-d of the flange 308 may be used as a connection part, and the optical module 300 may be fixed by joining it by other methods at the connection part. The other methods may be, for example, welding such as spot welding, soldering, brazing, pressure welding such as friction stir welding and friction pressure welding, diffusion bonding, sintering bonding, etc.

Industrial Applicability

[0051] As described above, the optical module according to the present invention can efficiently suppress optical coupling loss caused by warping of a base such as a fixing member, and can provide a more stable operation than the prior art. Such an optical module is expected to be applied to fields such as optical communication, particularly to optical communication amplification technologies and the like.

Explanation of Reference Numerals

[0052] 100, 200, 300 Optical module 101 Carrier 102 Optical element 103a-b Internal optical system 104 Package 105a-b External optical system 106a-b Optical fiber 107 Carrier fixing part 108, 308 Flange 109 Fixing member 110a-f, 310a-d Notch 500 Model

Claims

1. An optical module in which a package enclosing an optical device including an optical element is fixed via a flange, wherein the flange is provided with two connection portions on each of both side surfaces in a direction parallel to the optical axis direction of an optical signal that guides the optical element, and a distance between the centers of widths of each of the two connection portions is configured to be narrower than twice the length in the direction parallel to the optical axis direction of a carrier fixing portion that fixes the optical device inside the package. Optical module.

2. The connection portion is a notch, and the package is fixed by mechanical fastening via the flange. The optical module according to Claim 1

3. The optical module according to Claim 1, wherein the optical element is a non-linear optical element.

4. The material of the non-linear optical element is LiNbO 3 , LiTaO 3 , LiNb (x) Ta (1-x) O 3 (0 ≤ x ≤ 1), or the optical module according to claim 3, which is selected from materials containing at least one of Mg, Zn, Sc, and In as an additive in them.

5. The carrier fixing portion is a Peltier element, and the Peltier element is connected to a thermistor that measures the temperature of the optical element. The optical module according to Claim 1.

6. The optical module according to Claim 1, wherein the optical element has a waveguide structure.

7. The optical module according to Claim 1, wherein the optical device is a spatial optical coupling system device.

8. The optical module according to Claim 1, wherein the connection portion is disposed within a range of the length in the direction parallel to the optical axis direction of the carrier fixing portion.

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