JP4947212B2 - Manufacturing method of optical waveguide - Google Patents

Description

  The present invention relates to an optical waveguide manufacturing method and an optical component, and more particularly, an optical waveguide manufacturing method using an ultrashort pulse laser typified by a femtosecond laser, and an optical waveguide manufactured using the manufacturing method. It is related with the optical component which has.

In recent years, optical waveguides have been actively researched and developed as a leader of optical communications. Among them, an optical waveguide using a ferroelectric material made of a uniaxial crystal such as LiNbO ₃ (hereinafter referred to as “LN”) or LiTaO ₃ (hereinafter referred to as “LT”) has a refractive index changed by application of an electric field. Since the Pockels effect (electro-optic effect) is exerted, it is expected to be applied to a phase modulator, an optical switch, an isolator, and other various optoelectronic fields.

  Conventionally, a Ti diffusion method is known as a method for manufacturing this type of optical waveguide. In this Ti diffusion method, a Ti thin film is formed on a ferroelectric substrate by using a thin film forming method such as a sputtering method or an electron beam evaporation method, and heat treatment is performed at a temperature of about 1000 ° C. to thermally diffuse the Ti thin film. Then, a Ti diffusion layer having a high refractive index is formed on the ferroelectric substrate, thereby producing an optical waveguide. In uniaxial crystals such as LN and LT, birefringence occurs when light is incident, and it is divided into ordinary rays and extraordinary rays. However, the optical waveguide produced by the Ti diffusion method has the same refractive index for both ordinary and extraordinary rays. Can be increased to a degree, thereby confining light.

  However, in this Ti diffusion method, the waveguide must be patterned on the ferroelectric substrate using a photolithography technique or the like in addition to the thin film formation process and the thermal diffusion process described above, which complicates the manufacturing process. However, it has a drawback that it takes a long time and the manufacturing cost is increased.

  Therefore, recently, a laser technology that can be manufactured in a short time without the complicated manufacturing process as described above, particularly a manufacturing method using an ultrashort pulse laser has been attracting attention.

  For example, in Non-Patent Document 1, a femtosecond laser is used, and laser light emitted from the femtosecond laser is condensed inside a substrate made of LN (hereinafter referred to as an “LN substrate”) to provide an optical waveguide. Attempts have been made to produce.

This femtosecond laser can output an ultrashort pulse laser beam having a pulse time width (hereinafter referred to as “pulse width”) of a femtosecond (10 ⁻¹⁵ s) level at a predetermined repetition rate.

  In Non-Patent Document 1, a Ti: sapphire crystal is used as the laser oscillator, a pulse energy is 0.2 μJ, a repetition frequency is 1 kHz, and an objective lens having a magnification of 40 times and a numerical aperture of 0.65 is used. The LN substrate is irradiated with laser light having a depth of 50 to 150 μm from the surface of the LN substrate and a pulse width of 220 fs (femtosecond) and 1.1 ps (picosecond).

  According to this non-patent document 1, at the condensing position of the laser beam, it is damaged by heat from the laser beam. For this reason, a waveguide is not formed at the condensing position, but a distortion occurs around the condensing position, and this distortion increases the refractive index of the extraordinary ray (hereinafter referred to as “abnormal light refractive index”) ne. Yes. That is, the optical waveguide is formed so as to surround the damaged part.

  Further, in this Non-Patent Document 1, it is reported that the extraordinary refractive index ne increases as described above, but the refractive index of ordinary light (hereinafter referred to as “ordinary refractive index”) no has not changed. . That is, since the extraordinary refractive index ne increases, an optical waveguide of TM (Transverse Magnetic) light (p-polarized light) whose magnetic vector oscillation direction is perpendicular to the incident surface can be obtained. It has been reported that an optical waveguide of TE (Transverse Electric) light (s-polarized light) perpendicular to the incident surface could not be obtained.

  As other prior art, Non-Patent Document 2 uses an ultra-short pulse fiber laser (fiber chirp pulse amplification laser), sets the repetition frequency to 100-1500 kHz, and focuses the laser light inside the LN substrate. Attempts have been made to fabricate optical waveguides.

  According to Non-Patent Document 2, the laser beam is irradiated onto the LN substrate at the repetition frequency under the conditions of pulse energy of about 270 nJ and pulse width of about 600 fs. When the repetition frequency is 100 kHz, the condensing position is damaged and distortion due to stress occurs, but when the repetition frequency increases, the distortion gradually decreases, and at the repetition frequency of 700 kHz, the distortion is greatly reduced. It has been reported that distortion hardly occurs when the repetition frequency is 1000 kHz or more.

  Further, when waveguide confirmation is performed at a repetition frequency of 700 kHz, the ordinary light refractive index no increases and TE light waveguide is observed. This is because when the repetition frequency is increased to about 700 kHz, the generation interval of the ultrashort pulse is shortened, and as a result, the thermal relaxation time of the laser light is shortened and heat is accumulated, thereby increasing the ordinary light refractive index no. Seem.

  In Non-Patent Document 2, TM light waveguide was also observed, but this TM light is formed by optical waveguides different from TE light (for example, three optical waveguides arranged in the vertical direction in an LN substrate). In this case, the upper stage and the lower stage are TE optical waveguides and the middle stage is TM optical waveguides), and it is pointed out that TM light has a very large propagation loss.

J. Burghoff, S. Noltz, A. Tunnermann, "Origins of waveguiding in femtosecond laser-structured LiNbO3", Appl. Phys. A89, p.127-132, 2007 A.H.Nejadmalayeri, P. Herman, `` Rapid thermal annealing in high repetition rate ultrafast laser waveguide writing in lithium niobate '', Optics Express, 15, p. 10842-10854, 2007

  As described above, in Non-Patent Document 1, the extraordinary refractive index ne increases even when the LN substrate is irradiated with an ultrashort pulse laser, but the ordinary refractive index no does not change, and therefore TM light is guided. However, there is a problem that TE light is not guided and has polarization dependency.

  In Non-Patent Document 2, although it has been confirmed that TE light and TM light are guided, it is not possible to guide both TE light and TM light through the same optical waveguide. That is, in the same optical waveguide, only one of TE light and TM light can be guided, and similarly to Non-Patent Document 1, there is a problem that it has polarization dependency. Moreover, Non-Patent Document 2 also has a problem that the propagation loss of TM light is very large.

The present invention has been made in view of such circumstances, and even when an ultrashort pulse laser beam is used, an optical waveguide having a good cross-sectional shape and having no polarization dependency can be easily manufactured. and to provide a manufacturing how the optical waveguide can be.

  In the said nonpatent literature 1, distortion arises around the condensing position by irradiating the laser beam of an ultrashort pulse, and, thereby, the extraordinary-light refractive index ne is increasing. That is, it is considered that the formation of strain inside the uniaxial crystal ferroelectric substrate causes an increase in the extraordinary refractive index ne.

  On the other hand, in Non-Patent Document 2, by increasing the repetition frequency and shortening the generation interval of ultrashort pulses, the thermal relaxation time of the laser light is shortened and heat is accumulated, thereby increasing the ordinary light refractive index no. is doing. That is, the accumulation of heat is considered to cause an increase in the ordinary refractive index no.

The present inventors pay attention to such points and use LT having a melting point higher than that of LN for the substrate, and the pulse time width is 100 to 250 kHz so that heat is accumulated while remaining strain. After intensive research by irradiating the LT substrate with a laser beam of 100 fs or less, an ultrashort laser with a pulse energy of 1.5 μJ or more with a depth of 20 to 50 μm from the surface of the LT substrate as a condensing position. It was found that by irradiating light, an optical waveguide having a good cross-sectional shape of the optical waveguide and capable of guiding both TE light and TM light in the same waveguide can be obtained.

The present invention has been made on the basis of such knowledge, and the method of manufacturing an optical waveguide according to the present invention has a depth of 20 μm to 50 μm from the surface of the substrate with respect to the LT substrate. And irradiating the substrate with a laser energy having a pulse time width of 100 fs or less and a repetition frequency of 100 to 250 kHz to the substrate with a pulse energy of 1.5 μJ or more, and irradiating the substrate with the laser light. A light propagation portion that scans and has a refractive index higher than that of the substrate and guides both TE light and TM light is formed at the light collecting position.

  In the present invention, “ultrashort pulse” refers to a pulse having a femtosecond level pulse width.

  Furthermore, the optical waveguide manufacturing method of the present invention is characterized in that the laser beam emission source is a femtosecond laser.

According to the method for manufacturing an optical waveguide of the present invention, the depth of 20 μm to 50 μm from the surface of the LT substrate is the condensing position, the pulse time width is 100 fs or less, and the repetition frequency is 100 to 250 kHz . The substrate is irradiated with a laser beam emitted in number with a pulse energy of 1.5 μJ or more, and the substrate is scanned with the laser beam. The refractive index is higher than that of the substrate, and both TE light and TM light are guided. Since the wave propagation part is formed at the condensing position, an optical waveguide having a good cross-sectional shape and no polarization dependency can be manufactured. Therefore, it is possible to easily obtain an optical waveguide suitable for various optical components capable of rotating and switching the polarization plane. Moreover, since the condensing position is at least 20 μm or more, the condensing position has an appropriate depth from the surface of the LT substrate, and the substrate surface does not ablate even when irradiated with a laser.

  Furthermore, since the laser beam emission source is a femtosecond laser, the laser beam emission conditions can be easily adjusted, and without requiring a complicated manufacturing process such as the Ti diffusion method, A desired optical waveguide having no polarization dependency can be obtained at a low manufacturing cost.

By manufacturing an optical waveguide using the above-described manufacturing method, various desired optical components such as a phase modulator, an optical switch, and an isolator can be obtained inexpensively and easily.

It is a perspective view which shows one Embodiment of the optical component manufactured using the manufacturing method of the optical waveguide which concerns on this invention. It is a longitudinal cross-sectional view of FIG. It is the figure which showed typically the optical waveguide manufacturing apparatus used for the manufacturing method of the optical waveguide which concerns on this invention. It is a figure which shows an example of the pulse waveform output from a femtosecond laser. It is a figure which shows the other example of the pulse waveform output from a femtosecond laser. It is the figure which showed typically the cross-sectional shape of the optical waveguide used as the evaluation reference | standard of the cross-sectional shape of an Example sample. It is the figure which showed typically the apparatus used for confirmation of the polarization independence of an Example sample. It is a CCD image of the sample number 11 when a half-wave plate is set to a 1st position and waveguide confirmation is carried out. It is a CCD image of the sample number 11 when a half-wave plate is set to a 2nd position and waveguide confirmation is carried out. It is a CCD image of sample number 5 when the half-wave plate is set to the first position and the waveguide is confirmed. It is a CCD image of sample number 5 when the half-wave plate is set at the second position and the waveguide is confirmed.

Explanation of symbols

2 LT substrate 3 Optical waveguide 4 Femtosecond laser 5 Laser light

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view showing an embodiment of an optical component manufactured by using the method for manufacturing an optical waveguide according to the present invention, and FIG. 2 is a longitudinal sectional view thereof.

  That is, in the optical component 1, the optical waveguide 3 having both the ordinary light refractive index no and the extraordinary light refractive index ne higher than those of the LT substrate 2 is formed inside the substrate (LT substrate) 2 made of LT crystal. .

  Specifically, when the depth d from the main surface (front surface) 2a of the LT substrate 2 is set as a laser beam condensing position, the optical waveguide 3 is set to a position within 50 μm. The LT substrate 2 is formed in parallel with the main surface 2a, and the cross-sectional shape is circular or elliptical so that TM light and TE light can propagate with high efficiency.

  FIG. 3 is a schematic view schematically showing an embodiment of an optical waveguide manufacturing apparatus used for manufacturing the optical waveguide 3.

  That is, the optical waveguide manufacturing apparatus includes a femtosecond laser 4 as an ultrashort pulse laser, and an objective lens 6 that condenses the laser light 5 from the femto laser 4 at a condensing position F of the LT substrate 2. Yes.

  Specifically, the femtosecond laser 4 includes an ultrashort pulse oscillator 7 having a laser medium such as a Ti: sapphire crystal, and a pulse expander that temporarily extends the pulse width of the laser light obtained by the ultrashort pulse oscillator 7. 8, a pulse amplifier 9 for amplifying the pulse expanded by the pulse expander 8, a pump laser 10 for exciting the pulse amplifier 9, and pulse compression for compressing the pulse amplified by the pulse amplifier 9 into the ultrashort pulse The container 11 is provided as a main part.

  When laser light (for example, green light having a wavelength λ of 532 nm) from an excitation source (not shown) is input to the ultrashort pulse oscillator 7, the ultrashort pulse oscillator 7 outputs a femtosecond level (for example, 100 fs). ) Is output. That is, in the ultrashort pulse oscillator 7, the phases are synchronized so that a plurality of longitudinal modes interfere with each other, the phases are continuously oscillated while the phases are locked, and the ultrashort pulse is operated by overlapping the phases. The laser beam is generated.

  Since this laser beam has a low output energy, it is necessary to amplify the output energy. However, the laser beam itself has a very short pulse width as described above, and is sharp and has a high peak output. Accordingly, if amplification is performed in this state, various optical elements arranged in the optical path may be damaged. Accordingly, the pulse width of the laser beam is temporarily expanded to a picosecond level (for example, 100 ps) by the pulse expander 8 to suppress the sharp peak output, and then the excitation laser (for example, green light having a wavelength λ of 532 nm) is set. The output energy is amplified by the pulse amplifier 9 excited through the above. Thereafter, the pulse compressor 11 compresses the pulse width again to a femtosecond level (for example, 100 fs), and laser light having a high output energy and an ultrashort pulse width is emitted from the femtosecond laser.

  The objective lens 6 is configured by a condensing optical system that condenses the principal surface 2a of the LT substrate 2 at a position where the depth d is within 50 μm. A lens group designed for 40 can be used.

  Here, the depth d is set within 50 μm because when the depth d exceeds 50 μm, the cross-sectional shape of the optical waveguide 3 is indicated by the thickness direction of the LT substrate 2 (indicated by an arrow T in FIG. 3). This is because it becomes difficult to form the optical waveguide 3 having a desired cross-sectional shape. This is presumably because the influence of aberration occurs on the laser light passing through the LT substrate 2.

  The upper limit of the depth d is not particularly limited, but is preferably 20 μm or more. That is, when the depth d is shallower than 20 μm, when the LT substrate 2 is irradiated with the laser beam 5, so-called “ablation” occurs, and the surface of the LT substrate 2 may be destroyed. Therefore, the depth d is preferably 20 μm or more.

  In the present embodiment, the pulse energy of the ultrashort pulse emitted from the femtosecond laser 4 is set to 1.5 μJ or more. The reason will be described below.

  That is, for example, when the pulse energy is less than 0.5 μJ, since the pulse energy is too small, it is impossible to cause distortion effective for increasing the extraordinary refractive index ne. In this case, even if the repetition frequency is increased, effective heat accumulation is not sufficient to increase the ordinary refractive index no, and it is difficult to form the optical waveguide 3.

  In addition, when the pulse energy is increased to 0.5 or more and less than 1.5 μJ, a certain degree of distortion occurs at the condensing position F, and the extraordinary light refractive index ne can be increased. However, the cross-sectional shape becomes elongated and it becomes difficult to form the optical waveguide 3 having a desired cross-sectional shape. In addition, the pulse energy is low enough to accumulate heat, so that it is difficult to increase the ordinary light refractive index no even though the extraordinary light refractive index ne can be increased, and it has polarization dependence. It will be.

  Therefore, the pulse energy needs to be at least 1.5 μJ or more.

In addition, it is necessary to set a predetermined repetition frequency so that a desired distortion can be formed without damage to the condensing position F, and desired heat accumulation is performed. 1 to 250 kHz is set.

The reason will be described below.

  4 and 5 are examples showing the pulse waveform of the laser beam 5 emitted from the femtosecond laser 4, the horizontal axis is time t, and the vertical axis is the output intensity I. In the figures, t1 and t2 are pulses. The widths (fs), f1, and f2 indicate the repetition frequency (kHz), and t1 <t2 and f1> f2.

  When the repetition frequency is f and the pulse energy is E, the output energy P (energy per second) is expressed by Equation (1).

P = f · E (1)
Further, when the area of the condensing position F is S, the laser intensity I is expressed by Equation (2).

I = E / S · t (2)
Therefore, when the output energy P is constant, if the repetition frequency f is lowered, the pulse energy E increases, and the pulse shape is sharp and the output intensity I is very large as shown in FIG. That is, when the repetition frequency f is less than 100 kHz, for example, as low as 1 kHz as in Non-Patent Document 1, the pulse shape is sharp and the laser intensity I becomes very large. It is easily damaged by heat and is not preferable. In addition, since the pulse generation interval is long in this case, the heat relaxation time due to the laser light irradiation is also long, and therefore no heat is accumulated, so that the ordinary light refractive index no cannot be increased.

  On the other hand, for example, when the repetition frequency f is increased to 100 kHz or higher, the pulse energy E is relatively small in the range of at least 1.5 μJ, and the laser intensity I is also small as shown in FIG. Will also be moderate.

  In addition, in this embodiment, the LT substrate 2 is used instead of the LN substrate described in Non-Patent Documents 1 and 2, so that even if the repetition frequency is 100 kHz, damage due to heat is eliminated. Thus, only distortion can be formed, and the extraordinary light refractive index ne can be increased.

  That is, the melting point of the LN substrate is 1180 ° C., whereas the melting point of the LT substrate 2 is as high as 1650 ° C. Thus, in the case of the LN substrate, since the melting point is as low as 1180 ° C., it is considered that when irradiated with laser light having a sharp and high output intensity I, it is more easily damaged by heat than the LT substrate.

  On the other hand, the LT substrate 2 has a high melting point and excellent heat resistance as compared with the LN substrate, and is not easily damaged by the heat of laser irradiation. That is, even if the repetition frequency is 100 kHz, unlike the LN substrate, it is considered that only distortion can be formed without being damaged by heat.

  In addition, by setting the repetition frequency to 100 kHz or more, the pulse generation interval becomes longer, so that the heat relaxation time is shortened. As a result, heat is easily accumulated, and the ordinary light refractive index no can be increased. It becomes.

  By setting the repetition frequency to 100 kHz or higher in this way, only distortion remains without being damaged by heat, and the heat relaxation time is shortened to accumulate heat.

  As a result, both the ordinary light refractive index no and the extraordinary light refractive index ne can be increased, and the polarization-independent optical waveguide 3 having no polarization dependence can be formed.

  The upper limit of the repetition frequency f is not particularly limited, but is preferably 250 kHz or less practically.

  Also, the pulse width t of the ultrashort pulse is not particularly limited as long as it is a femtosecond level, but is preferably 100 fs or less in order to irradiate the condensing position F with a desired sharp pulse.

  Thus, in this embodiment, the ultrashort pulse laser beam having a pulse energy of 1.5 μJ or more is irradiated to the LT substrate 2 with a predetermined repetition frequency (preferably 100 to 250 kHz), and the LT substrate By scanning 2, an optical waveguide 3 capable of guiding both TE light and TM light can be formed.

  That is, according to the present embodiment, the depth within 50 μm from the surface of the LT substrate 2 is defined as the condensing position F, the pulse width of the ultrashort pulse (preferably 100 fs or less), and a predetermined repetition frequency ( Preferably, the substrate is irradiated with a laser beam emitted with a wave of 100 to 250 kHz with a pulse energy of 1.5 μJ or more, and the substrate is scanned with the laser beam, so that a light propagation portion having a refractive index higher than that of the substrate. Is formed at the light condensing position, so that an optical waveguide 3 having a good cross-sectional shape and capable of guiding both TE light and TM light can be obtained, thereby producing an optical waveguide 3 having no polarization dependency. Thus, the optical waveguide 3 suitable for various optical components that can rotate and switch the polarization plane can be obtained.

  Further, since the condensing position F has the predetermined depth of at least 20 μm or more, the condensing position F has an appropriate depth from the main surface 2a of the LT substrate 2, and even if laser irradiation is performed, the LT The surface of the substrate 2 does not ablate.

  Furthermore, since the emission source of the laser beam 5 is a femtosecond laser, it is possible to easily control the emission condition of the laser beam, and in a short time without requiring a complicated manufacturing process such as the Ti diffusion method. A desired optical waveguide can be obtained at a low manufacturing cost.

  And since it has the optical waveguide manufactured using the above-mentioned manufacturing method, it becomes possible to obtain desired various optical components, such as a phase modulator, an optical switch, and an isolator, cheaply and simply.

  The present invention is not limited to the above embodiment. In the above embodiment, a femtosecond laser using a Ti: sapphire crystal as a laser medium is used as the ultrashort pulse laser. However, any laser capable of emitting an ultrashort pulse laser beam may be used. A fiber laser can also be used.

  Next, examples of the present invention will be specifically described.

  Using the manufacturing apparatus of FIG. 3 described above, the optical system is adjusted so that the condensing position is 20 μm, 50 μm, and 100 μm from the substrate surface, and the z-cut LT substrate is irradiated with laser light to obtain sample numbers 1 to 1. Eighteen samples were prepared.

  As the femtosecond laser, a Ti sapphire mode-locked laser regenerated and compressed with Coherent RegA9000 was used.

  The laser light irradiation conditions and the specifications of the objective lens are as follows.

[Laser irradiation conditions]
Pulse width: 82fs
Repeat frequency: 100 kHz or 250 kHz
Pulse energy: 0.5 μJ, 1.0 μJ, 1.5 μJ, or 2.0 μJ
Scanning speed: 100 μm / s
[Objective lens specifications]
Magnification: 50 times Numerical aperture: 0.8
Next, the cross section of each sample of the sample numbers 1-18 was grind | polished and the cross-sectional shape was observed with the polarizing microscope.

  FIG. 6 is a diagram schematically showing the cross-sectional shape.

  In this embodiment, the optical waveguide is sufficiently formed from a sample whose cross-sectional shape is symmetric or substantially symmetric and whose ratio a / b between the major axis a and the minor axis b is less than 1/1 to 3/1. A sample having an asymmetrical shape with a clear cross-sectional shape and a ratio a / b of 3/1 or more is marked with a Δ mark because the optical waveguide is temporarily formed although it is insufficient. A sample in which formation of a waveguide was not recognized at all was marked with x, and the cross-sectional shape was evaluated.

  Moreover, about each said sample, the laser beam was irradiated to the sample, the state was imaged, and polarization independence was evaluated.

  FIG. 7 is an apparatus diagram schematically showing an apparatus for confirming polarization independence.

  In this apparatus, a half-wave plate 14 for controlling the polarization direction and an objective lens 15 are disposed in an optical path 12 on the laser irradiation side, and a CCD camera 17 is disposed in an optical path 16 facing the laser irradiation side through a sample 13. In addition, an objective lens 18 is disposed. Then, the half-wave plate 14 is set to the first position and irradiated with laser light to check the waveguide state of the TM light, and then the half-wave plate 14 is rotated by 90 ° from the first position to obtain the second The position was set, and the waveguide state of TE light was confirmed.

  That is, first, a red He—Ne laser having a wavelength of 633 nm is transmitted through the half-wave plate 14 set at the first position, and then condensed by the objective lens 15 on the optical waveguide forming position in the sample 13. The state was imaged with the CCD camera 17, and it was investigated whether TM light waveguide was confirmed.

  Thereafter, the half-wave plate 14 is rotated by 90 ° from the first position and set to the second position, and the He—Ne laser is focused on the waveguide forming position in the sample 13 by the same method as described above. The state was imaged with the CCD camera 17, and it was investigated whether the TE light guide was confirmed.

  A sample in which both TM light and TE light are guided is marked with ◯, and a sample in which only one of TM light and TE light is guided is marked with △. Samples that could not be made were marked with x, and polarization independence was evaluated.

  Table 1 shows the evaluation results of repetition frequency, pulse energy, condensing position, cross-sectional shape, and polarization independence at the time of manufacturing the optical waveguide.

  Samples 1 to 12 are samples in which the repetition frequency is set to 250 kHz and the LT substrate is irradiated with laser light.

  Sample Nos. 1 to 3 were too small in pulse energy of 0.5 μJ, so that no optical waveguide was formed and no waveguide was confirmed.

  Sample Nos. 4 to 6 have a pulse energy of 1.0 μJ, and the LT substrate is irradiated with laser light with a pulse energy larger than that of Samples Nos. 1 to 3, but it is still insufficient to form a desired optical waveguide. Met. That is, although TM light guiding was confirmed, TE light guiding was not confirmed, and it was found that polarization dependence exists. This is because distortion is formed by the irradiation of the laser beam, and as a result, the extraordinary refractive index ne is increased and the TM light is guided. Therefore, it is considered that the ordinary light refractive index no does not increase and the TE light is not guided.

  Sample numbers 9 and 12 show the case where the pulse energies are 1.5 μJ and 2.0 μJ, respectively, and the condensing position is 100 μm. In this case, since the pulse energy is 1.5 μJ or more and has sufficient pulse energy, both the ordinary light refractive index no and the extraordinary light refractive index ne increase, and the TM light and the TE light are guided. It was confirmed and it was confirmed that it has polarization independence. However, the condensing position is as deep as 100 μm, so that the ratio a / b is 3/1, the cross-sectional shape becomes excessively long and the desired cross-sectional shape cannot be obtained.

  On the other hand, Sample Nos. 7, 8, 10 and 11 have a pulse energy of 1.5 μJ or more and a light condensing position of 20 μm and 50 μm, so that the cross-sectional shape is a desired shape and the polarization independent optical waveguide. It was confirmed that

  Sample numbers 13 to 18 are samples in which the repetition frequency is set to 100 kHz and the LT substrate is irradiated with laser light.

  Among these, since the sample numbers 15 and 18 have pulse energy of 1.5 μJ and 2.0 μJ, respectively, and sufficient pulse energy, both the ordinary light refractive index no and the extraordinary light refractive index ne increase, It was confirmed that TM light and TE light were guided and that they were polarization independent. However, since the condensing position is as deep as 100 μm, the ratio a / b is about 4/1, the cross-sectional shape becomes excessively long, and a desired cross-sectional shape cannot be obtained.

  In contrast, Sample Nos. 13, 14, 16 and 17 have a desired cross-sectional shape and a polarization-independent optical light because the pulse energy is 1.5 μJ or more and the focusing positions are 20 μm and 50 μm. It was confirmed that a waveguide was obtained.

  In addition, although the present inventors tried to produce a waveguide with a repetition frequency of 10 kHz, a desired good cross-sectional shape could not be obtained even if the other irradiation conditions of the laser were changed, and polarization-independent. It was not possible to obtain an optical waveguide having properties.

  FIG. 8 is a CCD image of sample number 11 when the half-wave plate 14 is set to the first position and the waveguide is confirmed, and FIG. 9 is a half-wave plate 14 set to the second position. It is a CCD image of the same sample at the time of waveguide confirmation. In the figure, the white portion is the portion where the light is guided.

  As is apparent from FIGS. 8 and 9, in sample number 11, it is possible to confirm both TM light and TE light waveguides, and therefore, it is found that the light has no knitting light dependency.

  On the other hand, FIG. 10 is a CCD image of sample number 5 when the half-wave plate 14 is set to the first position and the waveguide is confirmed, and FIG. 11 is a half-wave plate 14 set to the second position. It is a CCD image of the same sample when the wave is confirmed. As in FIGS. 8 and 9, the white portion is the portion where the light is guided.

  As can be seen from FIG. 10, in Sample No. 5, the TM light was guided, but the CCD image in FIG. 11 was true black, and it was found that the TE light was not guided.

Claims (2)

Laser light emitted from a substrate made of LiTaO _{3 having} a depth of 20 μm to 50 μm from the surface of the substrate, a pulse time width of 100 fs or less, and a repetition frequency of 100 to 250 kHz. Irradiating the substrate with a pulse energy of 1.5 μJ or more, scanning the substrate with the laser light, and providing a light propagation part having a higher refractive index than the substrate and guiding both TE light and TM light. A method of manufacturing an optical waveguide, wherein the optical waveguide is formed at the condensing position. 2. The method of manufacturing an optical waveguide according to claim 1 , wherein the laser beam emission source is a femtosecond laser .

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