JP2002267871A - Optical element and optical component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical waveguide shape of an optical element which enables satisfactory coupling with other optical waveguides independently of an end surface position. SOLUTION: An optical element 1 is arranged in the course of a coupling waveguide 2 formed on a substrate 5, and has an optical waveguide 3 which is optically coupled with the coupling waveguide 2 and has an optical axis inclined to the end surface normal on both end surfaces 4 inside. The optical waveguide 3 of the optical element 1 has a straight part in which the optical axis at both end surfaces 4 is inclined to the same side with respect to the end surface normal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical element and an optical component. In particular, the present invention relates to an optical waveguide structure and an assembly alignment mark structure of an optical device having a waveguide structure.

[0002]

2. Description of the Related Art When an optical element having a waveguide structure, such as a semiconductor optical amplifier or an optical modulator, is optically coupled to an optical fiber or an optical waveguide or the like, the optical element is caused by a refractive index mismatch with a medium in a coupling gap. Reflection occurs at the element end face.

In particular, in a semiconductor optical amplifier, reflected light is amplified, causing noise and distorting an optical signal to be amplified. For this reason, a structure for suppressing the reflection at the end face of the optical element has been considered. For example, it is generally described in a book on ordinary semiconductor lasers (Applied Physics Series "Semiconductor Laser", Kenichi Iga, edited by the Japan Society of Applied Physics, published by Ohmsha, P345).

(1) Example of Semiconductor Optical Amplifier Using Diagonal Stripes FIG. 7 shows a schematic diagram of a conventional semiconductor optical amplifier. In this semiconductor optical amplifier, the optical element 1 is mounted on an optical waveguide substrate 5,
Light enters and exits from the optical element 1 to the optical waveguide 2 on the optical waveguide substrate 5. Here, a linear optical waveguide (hereinafter, such an optical waveguide is called a stripe structure or a stripe optical waveguide) 3 whose optical axis is inclined with respect to the two cleavage end faces 4 is formed in the optical element 1. .

As shown in the figure, the light reflected at each cleavage end face 4 of the semiconductor optical amplifier is returned to the inside of the semiconductor, but the portion that does not couple with the optical waveguide 2 increases, and the semiconductor optical amplifier becomes noise. The amount of light amplified within is greatly reduced. In particular, by using such a module together with a non-reflective dielectric multilayer film, optical noise due to reflection can be sufficiently reduced.

Here, since the optical waveguide 3 of the optical element 1, the optical waveguide 2 on the optical waveguide substrate, and the medium between the two optical waveguides have different refractive indexes, the traveling light is refracted at the interface. I do. Therefore, the optical axis of the optical waveguide is set to be inclined so as to satisfy Snell's law with respect to the normal direction of the end faces of the optical waveguides of the optical waveguide 3 and the optical waveguide 2 so that the direction of refraction and the direction of the optical waveguide are aligned. Have been.

However, in such an optical device, it is difficult to adjust the cleavage position, and it is difficult to adjust the cleavage position.
A slight displacement of the cleavage position occurs. That is, in the conventional optical device in which the optical waveguide portion is tilted, when the length of the chip changes, the end face position of the optical waveguide of the chip changes and the optical axis shifts. For this reason, as shown in FIG. 7B, the position of the optical waveguide on the cleavage end face 4 of the optical element 1 cannot be determined,
As in the case of the optical axis 10a of the radiated light, a positional shift occurs between the optical waveguides 2a and 2b, making it difficult to perform passive alignment.

Here, “passive alignment” means
This method is simple and suitable for mass production, for example, a method of aligning the optical element 1 and the optical waveguide substrate 5 by aligning them with a positioning reference provided, and automatically recognizing the marks using marks or the like formed by fine processing. This misalignment, relative distance g ₀ between the two emission light is the design value, when essentially the deviation is in the cleavage position for emission interval from the optical element changes the g is to avoid Can not.

In other words, in the state shown in FIG. 7B where the interval becomes g, the optical waveguide 2a and the optical axis 10a of the radiated light can be moved in parallel in the x-axis + direction to make them coincide with each other, or the y-axis + In any case, the coupling between the other optical waveguide 2b and the optical axis 10b of the radiated light becomes worse even if the optical waveguide 2b is moved in the parallel direction.

If the optical element is rotated in the xy plane, the direction of the optical axis is shifted, and good coupling cannot be obtained. Therefore, when the length of the optical element deviates from the set value due to cleavage, the active alignment of the optical element must be performed so that the optical waveguide 3 and the optical waveguide 2 are coupled with minimum loss after the optical element is activated. I didn't get it.

(2) Example of a semiconductor optical amplifier using a window structure FIG. 8 shows a semiconductor optical amplifier using a window structure. here,
The “window structure” is a structure in which the optical waveguide 3 in the optical element 1 is eliminated just before the cleavage end face 4 of the chip. Is suppressed from being optically coupled to the optical waveguide. Also in this window structure, optical noise can be sufficiently reduced by using the antireflection dielectric multilayer film together.

However, in such an optical element 1, it is necessary to sufficiently suppress the reflection at the end face of the optical waveguide, and it is necessary to sufficiently control the process in the embedding step, and the production yield is lowered. was there. Further, considering the coupling with the optical waveguide / optical fiber 2 ′, the light propagates freely in the vicinity of the cleaved end face, so that the distance between the optical waveguide and the optical fiber 2 ′ to be effectively coupled increases. There is a problem that the coupling ratio is reduced.

In the above-described conventional optical device 1, since the optical waveguide 3 is formed obliquely with respect to the cleavage end face 4, active alignment must be performed in the assembling process.
In addition, when the window structure is used, there is a problem that the gap g (accurately taking into account the refractive index) between the optical waveguide 3 and the optical waveguide / optical fiber 2 'is widened, and the coupling efficiency is deteriorated. .

Further, in a semiconductor optical amplifier, when spontaneous emission light generated in the middle of an optical waveguide propagates in the same direction as the propagation of the optical waveguide, the spontaneous emission is reflected at the end face and further amplified. However, the above-mentioned prior art could not sufficiently suppress it.

[0015]

The above-mentioned conventional semiconductor device using the window structure and the optical device having the obliquely striped optical waveguide have a problem from the viewpoint of coupling and assembly with the optical waveguide and the optical fiber. . SUMMARY OF THE INVENTION An object of the present invention is to solve the problem that when the end face (cleavage) position of an optical element changes, the coupling between the optical element and another optical waveguide element deteriorates. The present invention proposes an optical waveguide shape of an optical element that can be satisfactorily coupled to another optical waveguide regardless of the optical component, and provides an optical component using the same and a method of manufacturing the same.

[0016]

According to a first aspect of the present invention, there is provided an optical component, wherein an optical waveguide optically coupled to the coupling waveguide is provided in the middle of the coupling waveguide formed on the substrate. An optical component having an optical element provided therein,
The optical waveguide has, on both end faces of the optical element, two linear portions inclined to the same side with respect to the end face normal,
The optical element has an element-side alignment mark parallel to the linear part for each linear part, and the substrate is inclined so as to satisfy Snell's law with respect to the optical axis of the coupling waveguide. A substrate-side alignment mark formed parallel to the optical axis and to be aligned with the element-side alignment mark is provided for each of the coupling waveguides.

An optical component according to a second aspect of the present invention that achieves the above object is the optical component according to the first aspect, wherein the element-side alignment mark is formed of first and second double stripes. The substrate-side alignment mark is composed of third and fourth double stripes, and the first to fourth double stripes have the same stripe interval.

According to a third aspect of the present invention, there is provided a method of manufacturing an optical component, comprising an optical waveguide which is optically coupled to the coupling waveguide in the middle of the coupling waveguide formed on the substrate. A method for manufacturing an optical component having an optical element disposed thereon, comprising, on both end surfaces thereof, an optical waveguide having two linear portions inclined to the same side with respect to the end surface normal, and Forming the optical element provided with parallel element-side alignment marks for each of the linear portions, the optical axis being inclined on the substrate so as to satisfy Snell's law with respect to the optical axis of the coupling waveguide. Forming a substrate-side alignment mark to be aligned with the element-side alignment mark for each of the coupling waveguides.

And a step of arranging the optical element at a predetermined position on the substrate by using the element-side alignment mark and the substrate-side alignment mark.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an optical component according to the third aspect of the present invention, wherein the element-side alignment marks include first and second alignment marks. And the substrate-side alignment mark is composed of third and fourth double stripes, and four end portions of the first and second double stripes on the end face of the optical element. Is the third and fourth
Arranging the optical element on the substrate so as to be positioned one point at a time on the two-piece stripe.

[Operation] According to the structure of the optical element of the first aspect, the reflection of the radiation end faces before and after the optical element is suppressed, and the optical component can be automatically assembled by the alignment mark.
According to the two-layered stripe of the second aspect, high-precision and simple automatic assembly can be performed. According to claim 3,
The process of mounting an optical element, the reflection of which at the front and rear radiation end faces is suppressed, on a substrate can be automated, and automatic assembly can be performed with high accuracy and ease.

[0022]

[First Embodiment] FIG. 1 shows a semiconductor amplifier using an optical waveguide structure according to a first embodiment of the present invention. As shown in FIG. 1, on the optical waveguide substrate 5, an optical element 1 is arranged in the middle of the optical waveguide 2. As the optical waveguide substrate 5, a substrate in which an element mounting portion was formed in the middle of the quartz-based planar optical waveguide 2 formed on Si was used.

The optical element 1 has an optical waveguide 3 between the cleaved end faces 4.
Having. The optical waveguide 3 optically couples with the optical waveguide 2 and the optical axis is inclined with respect to the normal direction of the cleavage end face 4. Further, the optical axes at the both end surfaces of the optical waveguide 3 in the present reference example have linear portions inclined to the same side with respect to the end surface normal. That is, the optical waveguide 3 is a bent optical waveguide that is composed of two straight portions inclined with respect to the normal to the end face and a straight portion connecting the straight portions, and is bent at two places.

According to the semiconductor amplifier having such a structure, optical coupling between the optical waveguide substrate 5 and the optical element 1 is possible without causing optical axis shift. The reasons are as follows. Optical axes 10 and 11 emitted from optical waveguides to be coupled with each other.
The substrate and the semiconductor optical amplifier are designed so that the angles θ and φ are equal. In this state, if the alignment is performed so that the respective optical axes coincide, a desired alignment is obtained.

As shown in FIG. 1B, such a positioning is performed at a point P ₀ at which the two optical axes 11 emitted from the waveguide substrate 5 are connected to each other, and at a point P ₀ between the two optical axes emitted from the optical waveguide of the semiconductor amplifier. The point P connecting the optical axis 10 is obtained, and the optical element 1 may be moved by the vector P → P ₀ . That is, if the optical element 1 is moved by a vector corresponding to the vector P → P ₀ , the optical axis of the emitted light always coincides with the optical axis of the design value. The above is the reason why the alignment is possible.

As described above, if the structure of Reference Example 1 is used,
Positioning with essentially no positional deviation other than a change in the optical waveguide end face interval due to cleavage is possible. In the semiconductor optical amplifier shown in FIG. that is, the deviation from the g ₀ to g is advantageous compared to generate a shift of the cleavage location. Further, in this reference example, when the spontaneous emission light of the optical semiconductor amplifier was measured, the spontaneous emission light induced in the mode not coupled to the optical waveguide was radiated out of the optical waveguide by the bent optical waveguide, and was close to the waveguide mode. Since the spontaneous emission light is attracted to the signal light, an optical semiconductor amplifier having an excellent signal / noise ratio in which the spontaneous emission light is suppressed can be manufactured.

Embodiment 1 FIG. 2 shows a semiconductor amplifier according to a first embodiment of the present invention. Here, on the optical waveguide substrate 5, two sets of stripes each formed by patterning gold in parallel with two optical axes emitted from the optical waveguide 2 were formed as substrate-side alignment marks 21.

In the optical element 1, two sets of stripes parallel to the optical waveguide 3 and having the same interval as the stripe-shaped marks on the optical waveguide substrate 5 were produced as element-side alignment marks 22. Here, in consideration of cleaving the semiconductor optical amplifier to adjust its outer shape, a groove etched by dry etching was used as an alignment mark. Alternatively, when the substrate has a mesa structure often used in a semiconductor laser or a semiconductor optical amplifier, a groove of the mesa structure may be directly used as a mark.

The alignment procedure in FIG. 2 will be described. First, as shown in FIG. 2B, the lower end surface position of the optical element 1 and the substrate-side alignment mark 21 are aligned. Since the intervals between the marks 21 are made equal, the position to be matched is uniquely determined. Further, the angle alignment between the optical waveguide substrate 5 and the optical element 1 in the in-plane direction can be realized by aligning the ends of the alignment marks 21 and 22.

That is, the two alignment marks 21 and
By aligning the two ends, the positions of the optical waveguide substrate 5 and the optical element 1 are automatically corrected. This angle adjustment is the same as the adjustment of the parallelism of the optical axes of the light emitted from the optical waveguides of the optical waveguide substrate 5 and the optical element 1. Thereafter, as shown by an arrow in FIG. 2C, the optical element 1 is moved along the substrate-side alignment mark 21 so that the gap between the element-side alignment marks 22 of the optical element 1 becomes the substrate-side alignment mark. What is necessary is just to find a place corresponding to the gap of 21.

The alignment mark 22 on the element side is
Although the stripes are equally spaced and parallel to the optical waveguide 3,
It is not always necessary to form a stripe, and a dot may be provided at the end. FIG. 3 illustrates a procedure for positioning using calculations. First, the same operation is performed for the same purpose as in FIG. That is, as shown in FIG. 3B, the optical element 1 is moved so that the end of the element-side alignment mark 22 and the end of the substrate-side alignment mark 21 are aligned on the lower side of the figure. At this time, since the alignment is performed at two points, the angle of the optical element 1 with respect to the optical waveguide substrate 5 is automatically corrected. Further, as shown in FIG. 3C, also on the upper side of the figure, the optical element 1 is moved so that the end of the element-side alignment mark 22 and the end of the substrate-side alignment mark 21 are aligned.

The distance traveled by the optical element 1 during these two alignments is calculated by the number of pulses applied to the optical element 1 and the motor of the fine movement drive system of the optical waveguide substrate 5 to obtain a vector V. Using the optical axis inclinations θ and φ determined as design values, d = (V _y −V _x tan θ) / (1 + tan θ / tan φ) w = dcot φ is calculated, and only the vector (d, w) When the optical element is moved from the alignment position, the alignment is completed.

When positioning is performed using the above calculations, the substrate-side positioning marks 21 do not necessarily have to be in the form of stripes, but may be in the form of dots.

Embodiment 2 FIG. 4 shows an optical waveguide structure according to a second embodiment of the present invention. In the first embodiment, in order to perform passive alignment, the alignment marks 21 and 22 are used to move in accordance with the cleavage position to perform alignment to an optimum position.

On the other hand, in the present embodiment, as shown in FIG. 4, the marks 23 and 24 are fixed at predetermined positions to optimize the coupling loss. The mark 23 is a normal alignment mark formed on the optical element, and the mark 24 is a normal alignment mark formed on the waveguide substrate 5. FIG.
As shown in (b), the optical axis 10a of the radiated light from the optical waveguide 2 that is obliquely incident on the end face is positioned at the cleavage position, that is, the projected position of the optical axis of the radiated light due to the cleavage end face 4 of the optical element 1. Change. This is because the position on the end face of the optical waveguide changes.

Therefore, this embodiment is realized by controlling the position of the optical waveguide end on the cleavage end face 4 and the emission angle.
That is, the optical element 1 is arranged in the middle or at the end of the optical waveguide 2 formed on the optical waveguide substrate 5, and optically coupled with the optical waveguide 2 so that the optical axis at both end faces 4 is inclined with respect to the normal to the end face. Waveguide 3 was formed in optical element 1, and optical waveguide 3 was designed so as to have a predetermined curved shape in which the optical axis direction of emitted light always coincided with the end face of optical waveguide 2.

Specifically, as shown in FIG. 4, the structure of the optical waveguide 3 was determined using the following differential equation. That is, when the spot position Y (x) of the radiated light projected on the y-axis is given at the position 4 of the end face of the optical element 1 (the variable is x), the optical waveguide of the cleavage end face 4 of the optical element to be obtained is given. 3 of the position as (x, y), the tilt of the optical waveguide 3 at the cleaved end face 4, tanψ = dy / dx Snell's law and its _{differential, n 0 sinθ = n c sinψ} n 0 cosθdθ = n c cosψdψ optical device A relationship between the position (x, y) of the optical waveguide 3 on the cleavage end surface 4 and the target position (0, Y (x)) expressed by the angle of the emitted light, and a relational expression when the relationship is shifted by the position dx of the end surface; tan θ = (y + Y (x)) / x tan (θ + dθ) = (y + dy + Y (x) + (dY / d
x) dx) / (x + dx) is a simultaneous differential equation to be solved.

FIG. 5 is a graph of the position and inclination coupling loss of the optical waveguide calculated by setting the shape of the optical waveguide based on the above equation. The physical property values and the structure values of the quartz optical waveguide and the semiconductor optical amplifier were used as parameters. Here, for simplicity,
The design was made such that Y (x) = constant = 0 so that the center of the light emitted from the optical element always hit the origin, which is the center of the optical waveguide.

As shown in FIG. 5B, it is possible to suppress the loss due to the cleavage shift relatively small as compared with the semiconductor optical amplifier having the stripe structure. As described above, by using the solution of the differential equation of the present reference example, the spot position of the radiated light can be adjusted irrespective of the position of the cleavage plane.
4, the optical element 1 can be aligned. Although not shown here, this optical waveguide structure is applicable not only to optical coupling between optical waveguides but also to focusing light of the optical waveguide on a specific target.

[Embodiment 3] FIG. 6 shows a semiconductor optical amplifier according to a third embodiment of the present invention. In this reference example, reference example 2
One end of the optical element 1 corresponding to the above structure is a non-reflection end 4 and the other end is a high reflectance end face 6 having a high reflectance.
The light incident from the non-reflection end 4 is reflected from the rear high-reflectance end face 6 and amplified.

At the non-reflection end 4, the structure of Reference Example 2 was adopted, and further, an anti-reflection coating made of a dielectric multilayer film was applied to realize a good low reflectance. Furthermore, the amplification of the spontaneous emission light was suppressed by the curved structure of the optical waveguide, and a good signal / noise ratio was realized. As described above, when light is reflected on one side and reflection is suppressed on one side, it was confirmed that the structure of this embodiment can provide a very good module. .

[0042]

As described above in detail with reference to the embodiments, according to the present invention, it is possible to manufacture an optical element which can be assembled and has excellent reflection suppression at the end face. Also,
According to the optical waveguide structure of the first aspect, a structure of an optical element that can be assembled by automatic recognition can be provided.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a semiconductor optical amplifier according to a first reference example of the present invention.

FIG. 2 is an explanatory diagram of a positioning method by parallel movement in the semiconductor amplifier according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a calculation-based alignment method for the semiconductor amplifier according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of an optical waveguide structure according to a second reference example of the present invention, in which the position and the emission angle of the optical waveguide are optimized.

FIG. 5 is a graph showing the shape and coupling efficiency of an optical waveguide structure with an optimized optical waveguide position and emission angle according to a second reference example of the present invention.

FIG. 6 is an explanatory diagram of a semiconductor optical amplifier module using an optical waveguide structure with an optimized optical waveguide position and emission angle according to a third reference example of the present invention.

FIG. 7 is an explanatory diagram of an optical waveguide structure using oblique stripes.

FIG. 8 is an explanatory diagram of an optical waveguide structure having a window structure.

[Explanation of symbols]

 Reference Signs List 1 optical element 2 optical waveguide 3 optical waveguide 4 cleavage end face 5 optical waveguide substrate 6 high reflectance end face 10, 11 optical axis of emitted light 11 alignment mark 21 substrate side alignment mark 22 element side alignment mark 23 substrate side alignment Mark 24 Element alignment mark

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasufumi Yamada 2-3-1 Otemachi, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Akira Himeno 2-3-1 Otemachi, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation F term (reference) 2H037 BA24 CA10 DA18 2H047 KA03 KA12 KB09 TA11 2H079 AA05 CA05 CA09 DA16 EA03 EA07 EA32 EA33 KA11 5F073 AB22 AB28 BA01

Claims (4)

[Claims] 1. An optical component in which an optical element internally provided with an optical waveguide that optically couples with the coupling waveguide is disposed in the middle of the coupling waveguide formed on a substrate, wherein the optical waveguide comprises: On both end faces of the optical element, the optical element has two linear portions inclined to the same side with respect to the normal of the end face, and the optical element has an element-side alignment mark parallel to the linear portion with the linear portion. The substrate is aligned with the element-side alignment mark formed parallel to the optical axis inclined to satisfy Snell's law with respect to the optical axis of the coupling waveguide. An optical component having a substrate-side alignment mark to be provided for each of the coupling waveguides. 2. The optical component according to claim 1, wherein the element-side alignment mark is composed of first and second double stripes, and the substrate-side alignment mark is third and fourth stripes. An optical component, characterized in that the first to fourth double-set stripes have the same stripe interval. 3. A method for manufacturing an optical component, wherein an optical element having an optical waveguide for optically coupling with the coupling waveguide is disposed in the middle of the coupling waveguide formed on the substrate, wherein both ends thereof are provided. An optical waveguide having two linear portions inclined on the same side with respect to the end surface normal, and an element-side alignment mark parallel to the linear portion for each of the linear portions. Forming an element, on the substrate, aligned with the element-side alignment mark formed parallel to the optical axis inclined to satisfy Snell's law with respect to the optical axis of the coupling waveguide. Forming a substrate-side alignment mark for each of the coupling waveguides; and arranging the optical element at a predetermined position on the substrate using the element-side alignment mark and the substrate-side alignment mark. Having A method for manufacturing an optical component, comprising: 4. The method for manufacturing an optical component according to claim 3, wherein the element-side alignment mark is composed of first and second double stripes, and the substrate-side alignment mark is a third and a second stripe. Four end portions of the first and second double-set stripes on the end face of the optical element are arranged one by one on the third and fourth double-set stripes. A method for manufacturing an optical component, comprising a step of disposing the optical element on the substrate so as to be located.