JP2016161915A - Optical waveguide device and optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide device and an optical device that can increase the near field diameter of a light in an optical transmission part of an optical transmission element and can reduce the length of an element of an optical waveguide substrate, in optical coupling of the optical waveguide substrate to another optical transmission element.SOLUTION: An optical waveguide substrate 1 includes: a supporting substrate 15; a clad 14 on the supporting substrate 5; and a core 2 on the clad 14 for propagating lights, having an entrance part 2a for receiving entrance of lights and an exit end surface 2b emitting the propagated lights. The exit end surface 2b of the core 2 has a concave part 5 recessed with respect to an exit-side end surface 14a of the clad 14.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical waveguide element and an optical device.

  An external resonator type semiconductor laser has been developed in which a diffraction grating is a component different from a semiconductor and a resonator is formed outside. This type of laser is a laser with good wavelength stability, temperature stability, and controllability. The external resonator includes a fiber Bragg grating (FBG) (Non-patent Document 1) and a volume hologram grating (VHG) (Non-patent Document 2). Since the diffraction grating is composed of a separate member from the semiconductor laser, it has the feature that the reflectance and resonator length can be individually designed, and it is not affected by the temperature rise due to heat generation due to current injection. Can be better. Further, since the temperature change of the refractive index of the semiconductor is different, the temperature stability can be improved by designing it together with the resonator length.

  Patent Document 1 (Japanese Patent Laid-Open No. 2002-134833) discloses an external resonator type laser using a grating formed in a quartz glass waveguide. This is to provide a frequency stabilized laser that can be used in an environment where the room temperature changes greatly (for example, 30 ° C. or more) without a temperature controller. Further, it is described that a temperature-independent laser in which mode hopping is suppressed and the oscillation frequency is not temperature-dependent is provided.

  There are the following three types of optical devices in which such an external resonator type light emitting device is further coupled to an optical waveguide element or an optical fiber array.

  In system 1, the grating element with a built-in semiconductor laser is optically aligned with the optical waveguide element and bonded (Patent Document 3).

  In method 2, a semiconductor laser light source and an optical waveguide element or optical fiber with a built-in grating are coupled and aligned (Patent Documents 4 and 5).

  In method 3, three components, a semiconductor laser light source, a grating element, and an optical waveguide element, are optically coupled (Patent Document 6).

  However, the method 3 requires submicron alignment, which is tact and difficult to commercialize. For this reason, a technique for integrating a grating in a semiconductor laser, a waveguide, or a fiber has been proposed as in methods 1 and 2.

JP2002-134833 Japanese Patent Application No. 2013-120999 US Patent Publication 2008 / 0291951A1 WO 2013-034813 JP 2000-082864 A JP2002-134833 Japanese Patent Application No. 2014-122161

IEICE Transactions C-II Vol.J81, No.7pp.664-665, July 1998 IEICE technical report LQE, 2005 Vol. 105, No. 52, pp.17-20 Furukawa Electric Times, January 2000, Issue 105, p24-29

  However, in order to stabilize the wavelength of a semiconductor laser using a grating, it is necessary to manufacture the semiconductor laser uniformly with an accuracy of 1 nm or less in a wafer at a grating pitch of several hundred nm. In order to form the grating pattern, an electron beam lithography apparatus, a stepper, and a nanoimprint apparatus are used, but the specifications of the warpage of the wafer and the surface irregularities are severe. For this reason, when a Bragg grating is built in a semiconductor laser light source or an optical waveguide, the yield of the grating formation becomes poor due to warpage and unevenness caused by the formation of these elements. Further, complicated masking is required because the fine structure of each element interferes with each other and the manufacturing process interferes. For these reasons, there is a demand for individually mounting three components as in method 3.

  As described in Patent Document 7, the present applicant has proposed to increase the tolerance of mounting at the time of mounting by devising the design between the grating element and the separate optical transmission element.

  However, further investigations have raised problems. That is, in order to improve the tolerance of light coupling between the emission part of the grating element and the incident part of the optical transmission element, it is necessary to increase the spot size of the emitted light from the grating element. On the other hand, if the spot size of the light in the Bragg grating is too large, it does not match the spot size of the light incident on the grating element. Therefore, it is necessary to reduce the spot size of the light in the Bragg grating to some extent.

  For this reason, in Patent Document 7, the present inventor has proposed to provide an enlarged taper portion that gradually increases the width of the ridge-type optical waveguide in the grating element in the light propagation direction. As a result, the width of the optical waveguide at the emission part of the grating element is expanded.

  However, when a tapered part that gradually increases the width of the ridge-type optical waveguide is provided, in order to obtain a desired light spot size (horizontal near-field diameter) at the output part, a considerable element length is actually required. Became. This is because there is a limit to how light spreads within the optical waveguide core. As a result, there is a problem that the element length of the grating element becomes long.

  An object of the present invention is to reduce the optical insertion loss to an optical transmission element by enabling the optical waveguide board to be shortened when optically coupling the optical waveguide board to a separate optical transmission element. is there.

The present invention provides a support substrate,
A clad provided on a support substrate, and an optical core provided on the clad and having a core for propagating light, the core having an incident part where light enters and an output end face from which propagated light is emitted A waveguide substrate,
A concave portion that is recessed with respect to the outgoing side end face of the cladding is formed on the outgoing end face of the core.

The present invention is an optical device comprising the optical waveguide substrate and an optical transmission element,
The optical transmission element includes an optical transmission unit having an incident part on which outgoing light from the outgoing end face of the core is incident.

  The inventor studied a method for shortening the element length of the optical waveguide substrate when optically coupling the optical waveguide substrate to a separate optical transmission element.

  In this process, the space between the output end face of the core of the channel-type optical waveguide and the optical transmission unit is increased to diffuse the outgoing light from the core in the lateral direction and enter the optical transmission member. I also thought about expanding the diameter. However, in this case, the phase of the light of each part is shifted when entering the optical transmission member, so that the insertion loss of the light into the optical transmission member increases.

For this reason, the present inventor, on the output end face of the core of the channel type optical waveguide,
It was conceived to form a recessed portion that was recessed with respect to the emission side end face of the cladding. As a result, the phase of the light of each part can be matched when entering the optical transmission member, and this makes it possible to reduce the insertion loss of light into the optical transmission member.

1 is a schematic plan view showing an optical waveguide substrate 1 and an optical transmission member 6 of the present invention. It is a perspective view which shows typically the optical waveguide board | substrate 1 of FIG. (A), (b), (c) is a cross-sectional view schematically showing the optical waveguide substrate 1, 1A, 1B, respectively. (A), (b), (c) is a cross-sectional view schematically showing the optical waveguide substrates 1C, 1D, and 1E, respectively. (A), (b) is a cross-sectional view which shows typically the optical waveguide substrates 1F and 1G, respectively. It is a cross-sectional view schematically showing the optical waveguide substrate 1H. It is a cross-sectional view schematically showing a so-called high mesa type optical waveguide. It is a top view which shows typically the coupling structure of a light source element, a grating element, and an optical transmission member. It is a top view which shows typically the coupling structure of a light source element, a grating element, and an optical transmission member. It is a top view which shows typically the coupling structure of a light source element, a grating element, and an optical transmission member. It is a side view which shows typically the coupling structure of a light source element, a grating element, and an optical transmission member. It is a figure which shows the calculation conditions in an Example. It is a graph which shows the result of the spreading experiment of light.

  The optical waveguide substrate of the present invention can be suitably used for optical filters, polarizing elements, optical modulators, and optical isolators in addition to grating elements.

  FIG. 1 shows a coupling structure of an optical waveguide substrate 1 and an optical transmission member 6 according to an embodiment of the present invention, and FIG. 2 is a perspective view of the optical waveguide substrate 1.

  In the optical waveguide substrate 1 of this example, an under cladding layer 14 is formed on a support substrate 15, and an optical material layer 16 is formed on the cladding layer 14. A pair of ridge grooves 3 are formed in the optical material layer, and a core 2 of a ridge type optical waveguide is formed between the ridge grooves 3. A thin portion 13 is formed under each ridge groove 3, and an extending portion 4 is formed outside each ridge groove 3. 2a is a light incident part, and 2b is a light emitting end face.

  On the other hand, in this example, the optical transmission member 6 is installed and is opposed to the emission end face of the optical waveguide substrate 1 with a predetermined interval. An optical transmission part 7 is formed on the optical transmission member 6, and an incident part 7 a of the optical transmission part 7 faces the emission end face 2 b of the core 2. In this example, the optical transmission part 7 is formed by a pair of ridge grooves 8, and an extension part 9 is formed outside each ridge groove 8.

In this example, the width W _out at the exit end surface 2 b of the core 2 is smaller than the width at the incident portion 7 a of the optical transmission unit 7. In this state, when the light 11 is emitted from the emission end face 2 b of the core 2, the light 11 is diffused while being spatially propagated and is incident on the incident portion 7 a of the optical transmission unit 7.

  Here, in this example, the exit end face 2b of the core 2 is recessed as compared with the end face 14a of the cladding, and the recess 5 is formed. Thereby, the phase shift when the light 11 reaches the incident part 7a of the optical transmission part 7 can be reduced, and the optical insertion loss to the optical transmission member can be reduced. An arrow A indicates a photoelectrolytic distribution of propagating light in the optical transmission unit.

  In a preferred embodiment, as shown in FIG. 1, the contour of the recess 5 forms a curved line. In this case, the optical waveguide substrate is observed from the main surface 1a of the optical waveguide substrate opposite to the support substrate. Thereby, the phase difference of the light when reaching the incident part of the optical transmission part can be further reduced.

  In a more preferred embodiment, when the optical waveguide substrate is observed from the main surface of the optical waveguide substrate opposite to the support substrate, the contour of the recess 5 is arcuate. Particularly preferably, the contour of the recess 5 is arcuate.

The depth H of the recess 5 when viewed from the emission side end face 14a of the clad 14 as the reference surface depends on the distance between the optical waveguide substrate and the optical transmission substrate and the mode field diameter. However, W _out / H is preferably 1 to 50, for example, and more preferably 5 to 30.

The curvature radius of the contour of the recess 5 is preferably W _out / 2 to 100 × W _out , and more preferably 3 × W _out to 15 × W _out . Specifically, when W _out is 3 μm, it is preferably 9 to 45 μm.

Hereinafter, the cross-sectional structure of the optical waveguide will be exemplified.
In the optical waveguide substrate 1 shown in FIG. 3A, an optical material layer 16 is formed on a support substrate 15 with an under cladding layer 14 interposed. For example, a pair of ridge grooves 3 are formed in the optical material layer 16, and a ridge-type optical waveguide core 2 is formed between the ridge grooves 3. The under cladding layer 14 and the atmosphere function as a cladding. Thin portions 13 are formed on both sides of the core, and extending portions 4 are formed outside the ridge grooves. In this example, the ridge groove does not reach the under cladding layer, and the thin portion 13 remains.

  In this case, the Bragg grating may be formed on the flat surface side of the optical material layer, or may be formed on the ridge groove side. From the viewpoint of reducing variations in the shapes of the Bragg grating and the ridge groove, it is preferable to provide the Bragg grating and the ridge groove on the opposite side of the optical material layer by forming the Bragg grating on the flat surface side.

  In the optical waveguide substrate 1 </ b> A of FIG. 3B, an over clad layer 20 that functions as a clad is formed on the optical material layer 16.

In the optical waveguide substrate 1B of FIG. 3C, the optical material layer 16 is formed on the support substrate 15 with the under cladding layer 14 interposed. For example, a pair of ridge grooves 3 are formed in the optical material layer 16, and a ridge-type optical waveguide core 2 is formed between the ridge grooves. In this example, a ridge groove is formed on the under cladding layer side. An over clad layer 20 is formed on the optical material layer 16.
An adhesive layer can be provided between the undercladding layer and the support substrate.

  In the ridge-type optical waveguide, the strip-shaped elongated core can be formed by removing the optical material under the ridge groove. In this case, the ridge-type optical waveguide is composed of an elongated core made of an optical material, and the cross section of the core forms a convex figure. There is an air layer around the core, depending on the underclad, overclad, and structure.

  The convex figure means that a line segment connecting any two points of the outer contour line of the core cross section is located inside the outer contour line of the core cross section. Examples of such figures include triangles, quadrangles, hexagons, octagons, and other polygons, circles, ellipses, and the like. As the quadrangle, a quadrangle having an upper side, a lower side and a pair of side surfaces is particularly preferable, and a trapezoid is particularly preferable.

  In the optical waveguide substrate 1 </ b> C of FIG. 4A, the under cladding layer 14 is formed on the support substrate 15, and the core 22 is formed on the under cladding layer 14. The cross section of the core (cross section in the direction perpendicular to the light propagation direction) has a trapezoidal shape, and the optical waveguide extends elongated. In this example, the upper side surface 22a of the core 22 is narrower than the lower side surface 22b.

  In the optical waveguide substrate 1 </ b> D of FIG. 4B, a clad layer 23 is formed on the support substrate 15, and a core 22 is embedded in the clad layer 23. The core 22 has a trapezoidal transverse cross section (cross section perpendicular to the light propagation direction), and the core extends elongated. In this example, the upper side surface 22a of the core 22 is narrower than the lower side surface 22b. The clad layer 23 includes an over clad 23 b on the core 22, an under clad 23 a, and a side clad 23 c that covers the side surfaces of the core 22.

  In the optical waveguide substrate 1 </ b> E of FIG. 4C, the cladding layer 23 is formed on the support substrate 15, and the core 22 </ b> A is embedded in the cladding layer 23. The cross section of the core 22A (the cross section in the direction perpendicular to the light propagation direction) is trapezoidal, and the core extends elongated. In this example, the lower side surface 22b of the core 22A is narrower than the upper side surface 22a. 23b is an overclad, and 23a is an underclad.

  In the optical waveguide substrate 1 </ b> F of FIG. 5A, the under cladding layer 14 is formed on the support substrate 15, and the core 22 is formed on the under cladding layer 14. The core 22 is included and buried by another clad 24. The clad 24 includes an over clad 24a and a side clad 24b. In this example, the upper side surface 22a of the core 22 is narrower than the lower side surface 22b.

  In the optical waveguide substrate 1 </ b> G of FIG. 5B, the under cladding layer 14 is formed on the support substrate 15, and the core 22 </ b> A is formed on the under cladding layer 14. The core 22 </ b> A is included and buried by another cladding layer 24. The clad layer 24 includes an over clad 24a and a side clad 24b. In this example, the lower side surface 24b of the core 24A is narrower than the upper side surface 24a.

  Furthermore, an optical waveguide substrate 1H having a form as shown in FIG. 6 can also be used. That is, the under cladding layer 14 is formed on the support substrate 15, and the core 22 is formed on the under cladding layer 14. And the groove | channel 28 is formed in the both sides of the core 22, and the extension part 4 is formed in the outer side of each groove | channel 28, respectively. In this example, the ridge groove is cut to the under cladding layer 14, and the thin portion below the groove does not remain.

  The shape of the optical waveguide may be a high mesa structure as shown in FIG. In this structure 62, an under cladding layer 63 is formed on a support substrate 61, a core 64 is formed thereon, and an over cladding layer 65 is formed thereon.

The width W of the optical waveguide core is the minimum value of the width in a cross-sectional view obtained by cutting the core with a cross section perpendicular to the propagation direction. T _s is the thickness of the core.

The refractive index of the core is preferably 1.8 or more, and more preferably 1.9 or more. The core material is preferably Ta ₂ O ₅ , ZnO, lithium niobate, lithium tantalate, aluminum oxide (Al ₂ O ₃ ), or TiO ₂ .

  The core may be formed by forming a film on the undercladding by a thin film forming method. Examples of such a thin film forming method include sputtering, vapor deposition, and CVD.

  The under clad and over clad function as the clad of the optical waveguide core. From this viewpoint, the refractive index of the underclad is preferably lower than the refractive index of the core, and the refractive index difference is preferably 0.2 or more, and more preferably 0.4 or more.

From such a viewpoint, examples of the material of the under clad and the over clad include SiO ₂ , aluminum oxide (Al ₂ O ₃ ), polyimide, and MgF.

  The specific material of the support substrate is not particularly limited, and examples thereof include glass such as lithium niobate, lithium tantalate, and quartz glass, quartz, and Si.

  The optical device of the present invention includes the optical waveguide substrate of the present invention and an optical transmission element, and the optical transmission element includes an optical transmission unit having an incident part on which light emitted from the exit end face of the core is incident. .

  8 to 10 each relate to an optical device according to the present invention. FIG. 11 is a side view of the optical device of FIG.

  The optical device schematically shown in FIG. 8 includes a light source 37 that oscillates semiconductor laser light, a grating element 31, and an optical transmission element 40. In this example, an optical waveguide element is used as the optical transmission element 40, but the optical waveguide of the optical transmission element can be changed to an optical fiber.

  The light source 37 and the grating element 31 may be mounted on a common substrate (not shown). Further, the grating element 31 and the optical transmission element 40 may be mounted on a common substrate (not shown).

  The light source 37 includes an active layer 38 that oscillates semiconductor laser light. A reflective film may be provided on the outer end face 38 a of the active layer 38. A non-reflective film or a reflective film may be formed on the end surface 38b of the active layer 38 on the grating element side.

An optical waveguide 35 is formed in the optical material layer 44 of the grating element 31. The optical waveguide 35 includes an incident side propagation part 33 without a diffraction grating, a grating part 32 provided with a Bragg grating, and an output side propagation part 34 without a diffraction grating. The emission side propagation part 34 includes a constant width part 34a adjacent to the grating part 32, a tapered part 34b in which the core width gradually increases, and an emission part 34c having a constant width. The core widths at the incident side propagation part 33 and the grating part 32 are W _in and W _gr , and the core width at the emission part 34 c is W _out .

  An optical transmission member 40 is installed so as to face the emission-side end face of the grating element 31. An optical waveguide 41 is formed in the optical transmission member 40. The optical waveguide 41 includes an incident portion 41a having a constant width, a tapered portion 41b in which the width of the optical waveguide is gradually reduced, and an emitting portion 41c having a constant width. Reference numeral 42 denotes an entrance surface, and 43 denotes an exit surface.

In this example, the width W _out of the exit end face 35b of the core of the grating element 31, the width W _gr of optical waveguide core in a Bragg grating _is larger than the core width W _in the entrance section. The horizontal direction of the near field diameter B _out of the mode field pattern at the output end face 35b of the core of the grating element 31 is larger than the horizontal direction of the near-field diameter B _in the entrance portion.

Further, in this embodiment, the horizontal direction of the near-field diameter D _out at the exit portion 41c of the optical transmission section 41 is smaller than the horizontal direction of the near-field diameter D _in the incident portion 41a. At the same time, the horizontal near-field diameter D _{in in} the optical transmission section 41a is larger than the horizontal near-field diameter B _out in the emission section 34c of the grating element 31.

In the device of FIG. 9, the light source element 37, the grating element 31A, and the optical transmission member 40A are optically coupled. In this example, an optical waveguide 35A is formed in the optical material layer 44 of the grating element 31A. The optical waveguide 35A includes an incident side propagation part 33A without a diffraction grating, a grating part 32, and an emission side propagation part 34A without a diffraction grating. The incident side propagation part 33A includes an incident part 33a having a constant width, a tapered part 33b in which the core width is gradually reduced, and a constant width part 33c having a constant width. Also, exit side propagating portion 34A is of constant width portion 34a and the core width _{W m} adjacent to the grating portion 32 is provided with a tapered portion 34d which gradually expanded. The core width in the incident portion 33a is _{W in,} the core width in the grating element 32 is _{W gr,} the maximum value of the core width at the exit portion 34d is _{W out.}

  An optical waveguide 41A is formed in the optical transmission member 40A. The optical waveguide 41A includes an incident portion 41a having a constant width, a tapered portion 41b in which the width of the optical waveguide is gradually reduced, and an emitting portion 41c having a constant width.

In this example, the width W _out of the output end face 35b of the core of the grating element 31A is larger than the width W _gr of the optical waveguide core in the Bragg grating. Further, in this embodiment, a near field diameter _{D out} of the water-direction at the output section 41c of optical transmission section 41A is smaller than the horizontal direction of the near-field diameter _{D in} the incident portion 41a. At the same time, the horizontal near-field diameter D _{in in} the optical transmission section 41a is larger than the horizontal near-field diameter in the emission section 34d of the grating element 31A.

In the device of FIG. 10, the light source element 37, the grating element 31B, and the optical transmission member 40B are optically coupled. In this example, an optical waveguide 35B is formed in the optical material layer 44 of the grating element 31B. The optical waveguide 35B includes an incident side propagation part 33 without a diffraction grating, a grating part 32, and an output side propagation part 34B without a diffraction grating. The emission side propagation part 34B includes a constant width part 34a adjacent to the grating part 32, a tapered part 34e in which the core width gradually decreases, and a constant width part 34f having a constant width. The core width in the incident portion 33a is _{W in,} the core width in the grating element 32 is _{W gr,} core width at the exit end face 35b is _{W out.}

  An optical waveguide 41B is formed in the optical transmission member 40B. The optical waveguide 41B includes an incident portion 41a having a constant width, a tapered portion 41b in which the optical waveguide width is gradually reduced, and an emitting portion 41c having a constant width.

In this example, the width W _out of the output end face 35b of the core of the grating element 31B is smaller than the width W _gr of the optical waveguide core in the Bragg grating. Further, in this embodiment, the horizontal direction of the near-field diameter _{D out} at the exit portion 41c of the optical transmission section 41B is smaller than the horizontal direction of the near-field diameter _{D in} the incident portion 41a. At the same time, the horizontal near-field diameter D _{in in} the optical transmission section 41a is larger than the horizontal near-field diameter B _out in the emission section 34d of the grating element 31B.

  The width of the optical waveguide core in the Bragg grating is set to be equal to the near-field pattern of the laser in order to increase the coupling efficiency with the semiconductor laser light source. The horizontal size of the near field of the semiconductor laser may be 2 μm to 7 μm, for example. In this case, the width of the optical waveguide core is set to 2 μm to 7 μm.

In a preferred embodiment, the horizontal near-field diameter D _{in at} the entrance of the optical transmission section is larger than the horizontal near-field diameter B _out at the exit end face of the core. In the optical waveguide substrate of the present invention, since the emitted light can be sufficiently diffused before reaching the incident portion of the light transmission member, the present invention can be applied particularly advantageously.

In the optical waveguide substrate of the present invention, by relatively increasing the optical waveguide core width W _out at the output end face of the optical waveguide, the near-field diameter of the mode field of the light beam at the output end face (horizontal direction) B _out Can be increased. As a result, the density of the light beam emitted from the grating element can be lowered, and the tolerance of the horizontal dimension when the emitted light is coupled to the optical transmission element can be improved. This significantly improves the productivity when the grating element and the optical transmission element are optically assembled.

However, if by increasing the near-field diameter D _in improving the margin for the optical axis deviation during alignment at the entrance portion of the optical transmission unit, the near field diameter when exiting from the optical transmission element to the outside too large Sometimes. In this case, as in this example, an emission part having a smaller near field diameter _Dout can be provided. In this case, it is preferable from the viewpoint of loss reduction to provide a taper portion where the near field diameter gradually decreases between the incident portion and the emission portion.

Near field diameter (horizontal direction) B _out at the output end face of the optical waveguide substrate of the present invention is preferably at least 5 [mu] m, more preferably not less than 7 [mu] m, the best least 10 [mu] m. Further, B _out is preferably 20 μm or less.

From the viewpoint of the present invention, the near field diameter (horizontal direction) D _{in in} the optical transmission section is preferably 5 μm or more, and more preferably 7 μm or more.
D _in / B _out is preferably 1.1 or more, and more preferably 1.2 or more, from the viewpoint of coupling the light emitted from the optical waveguide device of the present invention to the optical transmission device.

In a preferred embodiment, the width of the incident part of the optical transmission part is 1.2 times or more and 1.3 times or more of the width W _out of the exit end face of the core.

  The distance G (FIGS. 1, 8, 9, and 10) between the incident part of the optical transmission part and the exit end face of the core is 0.1 μm or more and 3 μm or less. This allows the diffusion of the light beam emitted from the exit end face of the core. Can also be promoted. From this viewpoint, it is more preferable that the distance between the incident part of the optical transmission part and the exit end face of the core is 3 μm or more. Also, if the distance between the incident part of the optical transmission unit and the exit end face of the core is too large, the optical insertion loss tends to increase.From this point of view, the incident part of the optical transmission part and the exit end face of the core Is preferably 20 μm or less.

  The near field diameter of the laser beam in the horizontal and vertical directions is measured as follows.

Measure the light intensity distribution of the laser beam and measure the width where the intensity distribution is 1 / e ² (e is the base of natural logarithm: 2.71828) with respect to the maximum value (usually equivalent to the center of the core). This is generally defined as the near field diameter. In the case of laser light, the near field is defined because the size differs in the horizontal and vertical directions of the laser element. When it is concentric like an optical fiber, it is defined as a diameter.
In the measurement of the light intensity distribution, the light intensity distribution of the laser light spot can be generally obtained by beam profile measurement using a near-infrared camera or light intensity measurement using a knife edge.

  As the light source, a laser with a highly reliable GaAs or InP material is suitable. As an application of the structure of the present application, for example, when a green laser that is the second harmonic is oscillated using a nonlinear optical element, a GaAs laser that oscillates near a wavelength of 1064 nm is used. Since GaAs-based and InP-based lasers have high reliability, a light source such as a one-dimensionally arranged laser array can be realized. It may be a super luminescence diode or a semiconductor optical amplifier (SOA). In addition, the material and wavelength of the active layer can be selected as appropriate.

Note that a method for stabilizing power by a combination of a semiconductor laser and a grating element is disclosed below.
(Non-Patent Document 3: Furukawa Electric Times, January 2000, No. 105, p24-29)

  The optical waveguide is obtained by, for example, physical processing and molding by cutting with an outer peripheral blade or laser ablation.

The Bragg grating can be formed by physical or chemical etching as follows.
As a specific example, a metal film such as Ni or Ti is formed on a high refractive index substrate, and windows are periodically formed by photolithography to form an etching mask. Thereafter, periodic grating grooves are formed by a dry etching apparatus such as reactive ion etching. Finally, it can be formed by removing the metal mask.

  The optical transmission element may be an optical waveguide element or an optical fiber array. The optical transmission element may be a harmonic generation element such as a second harmonic generation element, or may be a light control element such as an optical modulation element, a polarization element, an optical amplifier, an optical delay element, or an optical memory.

Example 1
The optical waveguide substrate described with reference to FIGS. 1, 2, and 3B was produced.
Specifically, a SiO ₂ layer to be the under-cladding layer 14 is formed on the support substrate 15 made of quartz by a sputtering apparatus, and a Ta ₂ O ₅ film is formed thereon to a thickness of 1.2 μm. An optical material layer of 1.2 μm was formed.

Next, Cr was formed on the optical material layer, and after applying a resist, an optical waveguide pattern was prepared by an EB drawing apparatus. Thereafter, a ridge waveguide having a width W of 3 μm and a groove depth of 0.6 μm was formed by fluorine-based reactive ion etching using the Cr pattern as a mask. Further, an SiO ₂ layer to be the over clad layer 20 was formed by 0.5 μm sputtering.

  In addition, in order to form a dent in the exit portion of the optical waveguide, Cr is again formed on the substrate, a resist is applied, and a width of 4 μm and a dent amount of 0 are set based on the center of the waveguide width by EB exposure. A pattern of 3 μm was formed. Thereafter, the over cladding layer and the optical material layer were similarly etched by fluorine-based reactive ion etching.

  Finally, a plurality of elements were cut side by side with a dicing apparatus, and the end surfaces on the incident side and the emission side were optically polished. At this time, it was controlled and processed so as to be terminated before 0 to +3 μm so as not to remove the dent on the exit end face. Further, 0.1% AR coating was formed on both end faces, and the chip was cut to produce an optical waveguide device as shown in FIGS. The element size was 1 mm wide x 10 mm long.

  The recess 5 has an arc shape with a center on the center line of the waveguide width and a radius of 20 μm. Thereby, it is recessed by 0.3 μm from the end face of the waveguide.

  About this element, the optical insertion loss and the spread of the spot shape in the horizontal direction were measured using a semiconductor laser with a wavelength of 830 nm. The spread of the spot shape in the horizontal direction was measured as follows. That is, as shown in FIG. 12, a light receiving side optical waveguide having a horizontal near-field pattern of 1 μm (ridge width 1 μm) is placed at a position 20 μm away from the emission end face of the optical waveguide, and the light incident on this optical waveguide The light intensity of was measured. Then, the light intensity measurement was repeated for each shift position while the optical waveguide on the light receiving side was shifted by 0.2 μm in the horizontal direction. In this way, the light spreading characteristics were measured.

Here, the light spreading width was defined as the width of the horizontal position where 1 / e ² lowers from the maximum value of the light intensity in the spreading characteristic.
As a result, the optical insertion loss was 1.0 dB, and the spread width was as large as 15.2 μm.

(Example 2)
An optical waveguide substrate was fabricated in the same manner as in Example 1.
Specifically, a SiO ₂ layer to be an under cladding layer 14 is formed on a support substrate 15 made of quartz by a sputtering apparatus, and a Ta ₂ O ₅ film is formed thereon to a thickness of 1.2 μm to form an optical material layer. Formed.

  Next, Cr was formed on the optical material layer, and after applying a resist, an optical waveguide pattern was prepared by an EB drawing apparatus. Thereafter, a ridge waveguide having a width W of 3 μm and a groove depth of 0.6 μm was formed by fluorine-based reactive ion etching using the Cr pattern as a mask.

Further, in order to form a dent on the exit end face of the optical waveguide, Cr is again formed on the substrate, a resist is applied, and a width of 4 μm with the center of the waveguide width as a base point by EB exposure is obtained. A 3 μm pattern was formed. Thereafter, the optical material layer was similarly etched by fluorine-based reactive ion etching. Thereafter, an overcladding layer made of SiO _{2 was formed} to a thickness of 2 μm so as to cover the optical material layer.

  Finally, a plurality of elements were cut side by side with a dicing apparatus, and the end surfaces on the incident side and the emission side were optically polished. At this time, it was controlled and processed so as to be terminated before 0 to +3 μm so as not to scrape the concave portion on the emission end face. Further, 0.1% AR coating was formed on both end faces, and the chip was cut to produce an optical waveguide substrate. The element size was 1 mm wide x 10 mm long.

In the same manner as in Example 1, the optical insertion loss and the spread of the spot shape in the horizontal direction of the optical waveguide substrate of this example were measured.
As a result, the optical insertion loss was 1.2 dB, and the spread width was 15.1 μm.

(Example 3)
The optical waveguide substrate described with reference to FIGS. 1, 2, and 6 was produced.
Specifically, in the same manner as in Example 1, a SiO ₂ layer serving as an under-cladding layer is formed on a support substrate 15 made of quartz by a sputtering apparatus, and Ta ₂ O ₅ is formed thereon with a thickness of 1.2 μm. An optical material layer was formed by forming a film.

Next, Cr was formed on the optical material layer, and after applying a resist, an optical waveguide pattern was prepared by an EB drawing apparatus. Thereafter, a ridge waveguide having a width of 3 μm and a groove depth of 1.2 μm was formed by fluorine-based reactive ion etching using the Cr pattern as a mask. Further, an over clad layer made of SiO ₂ was formed by 0.5 μm sputtering.

  Further, in order to form a dent in the light emitting portion of the optical waveguide, a Cr film is formed again on the substrate, a resist is applied, and a width of 4 μm and a dent amount of 0.3 μm are obtained from the center of the waveguide width by EB exposure. Pattern was formed. Thereafter, the over clad layer and the optical material layer were similarly etched by fluorine-based reactive ion etching.

  Finally, a plurality of elements were cut side by side with a dicing apparatus, and the end surfaces on the incident side and the emission side were optically polished. At this time, it was controlled and processed so as to be terminated before 0 to +3 μm so as not to remove the dent on the exit end face. Further, 0.1% AR coating was formed on both end faces, and the chip was cut to produce an optical waveguide device. The element size was 1 mm wide x 10 mm long.

Next, in the same manner as in Example 1, the optical insertion loss and the spread of the spot shape in the horizontal direction of the optical waveguide substrate were measured.
As a result, the optical insertion loss is 1.0 dB and the spreading width is 15.1 μm.

(Comparative Example 1)
An optical waveguide substrate was produced in the same manner as in Example 1.
However, in this example, the recess is not formed on the exit end face of the optical waveguide core, and the exit end face is flat.

In the same manner as in Example 1, the optical insertion loss of the optical waveguide substrate and the spread of the spot shape in the horizontal direction were measured.
As a result, the optical insertion loss is 1.0 dB and the spread width is 6 μm.

(Mode profile calculation result)
FIG. 13 shows the result of calculating a mode profile 20 μm ahead from the exit end face of the core when the depth H of the recess is changed. It was found that when the depth H of the concave portion is increased, the mode size in the horizontal direction is increased.

Claims (10)

Support substrate,
A clad provided on the support substrate, and a core for propagating light provided on the clad, the core having an incident part on which the light is incident and an exit end face for emitting the propagating light. An optical waveguide substrate,
An optical waveguide substrate, wherein a concave portion recessed with respect to an output side end surface of the clad is formed on the output end surface of the core.   The optical waveguide substrate according to claim 1, wherein when the optical waveguide substrate is viewed from a main surface opposite to the support substrate, the contour of the concave portion forms a curved line.   The optical waveguide substrate according to claim 2, wherein when the optical waveguide substrate is viewed from a main surface opposite to the support substrate, an outline of the concave portion is an arc shape.   The optical waveguide substrate according to any one of claims 1 to 3, wherein the core includes a ridge portion formed by at least a pair of ridge grooves.   The optical waveguide substrate according to any one of claims 1 to 3, wherein a cross section of the core has a convex shape.   It is a grating element provided with a Bragg grating, The optical waveguide board | substrate as described in any one of Claims 1-5 characterized by the above-mentioned. An optical device comprising the optical waveguide substrate according to any one of claims 1 to 6 and an optical transmission element,
The optical device, wherein the optical transmission element includes an optical transmission part having an incident part on which outgoing light from the outgoing end face of the core is incident.   The optical device according to claim 7, wherein a horizontal near-field diameter at the incident portion of the optical transmission unit is larger than a horizontal near-field diameter of the core at the emission end face of the core.   9. The optical device according to claim 7, wherein a distance between the incident part of the light transmission part and the emission end face of the core is 3 μm or more. 10. The optical device according to claim 7, wherein a width of the incident portion of the light transmission portion is 1.2 times or more a width of the core at the emission end face. .

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