KR100878978B1 - Method of Manufacturing Periodic Poled Lithium Niobate Waveguide Device - Google Patents

Abstract

Disclosed is a method of manufacturing a PPLN (Periodic Poled Lithium Niobate) waveguide device having nonlinear characteristics. Ultra-short laser is irradiated to PPLN to form waveguide inside. The driving stage is moved using a processing apparatus, and a laser is irradiated to a predetermined region of the PPLN. By adjusting the pulse intensity of the irradiated laser light source to adjust the refractive index of the waveguide formed inside the PPLN. In addition, by adjusting the processing conditions such as the intensity of the laser, the size of the beam, the focal length, it is possible to adjust the amount and shape of the refractive index change of the waveguide.

Description

Method for manufacturing PPIEL waveguide device using laser {Method of Manufacturing Periodic Poled Lithium Niobate Waveguide Device}

1 is a block diagram showing an example of a PPLN waveguide device manufacturing apparatus using a laser according to a preferred embodiment of the present invention.

2 is a measurement photograph of a PPLN waveguide device according to a preferred embodiment of the present invention.

3 is a second harmonic wave generation experiment apparatus using the PPLN waveguide device manufactured by the ultra-short pulse laser.

4 is a second harmonic curve measured by varying the wavelength of the external resonator laser 400 in the second harmonic wave generation experiment apparatus of FIG.

Explanation of symbols on the main parts of the drawings

100: laser light source 120: beam transmission system

140: beam splitter 160: condenser

180: drive stage

200: PPLN (Periodic Poled Lithium Niobate)

210: CCD camera 300: PPLN element

310: PPLN waveguide 400: external resonator laser

410: computer 420: polarization maintaining optical fiber

430 lens 440 silicon detector

The present invention relates to a waveguide, and more particularly to the manufacture of a waveguide device using a laser.

The development of periodic polarization reversal technology, developed in the early 1990s, paved the way for nonlinear optical research. The development of reproducible periodic polarization reversal techniques at room temperature enabled the quasi-phase matching (QPM) technique proposed by Armstrong et al. In 1962, especially in spite of high nonlinear coefficients. The use of the nonlinear coefficient component d ₃₃ of LiNbO ₃ , which had not been used due to the problem, was enabled, leading to the position of the non-linear optical material that is most produced and consumed LiNbO ₃ .

Recently, research on nonlinear optical integrated devices using LiNbO ₃ has been actively conducted. LiNbO ₃ An integrated device can reduce the size of the device by using an integration of a waveguide, a microelectrode, etc., and has a significantly higher nonlinear efficiency than a bulk nonlinear device. The development of such high efficiency nonlinear optical integrated devices has been made possible by efficient optical waveguide fabrication technology. LiNbO ₃ on The optical waveguide technology used is mainly an annealed proton exchange (APE) waveguide and a titanium diffusion waveguide, and the dual Ti diffusion waveguide can simultaneously wave TE and TM waves, and thus not only the nonlinear optical It is widely used for various elements using optical.

Periodically polarized inverted Ti: LiNbO ₃ (Ti: PPLN: titanium-indiffused periodically poled LiNbO ₃ ) Waveguide devices have a higher conversion rate and form-independent conversion efficiency than other types of all-optical signal processing devices, such as low cross talk and high transmittance in the optical communication wavelength band. It has the advantages of meeting many of the requirements for fiber optic communications. All-optical signal processing using Ti: PPLN waveguide devices includes self phase modulation and pulse compression, optical sampling, optical parametric amplification, and optical code division multiplexing (OCDMA). ), Wavelength conversion, optical gate switch, and quantum information processing.

A typical Ti: PPLN waveguide device is fabricated using photolithography with a Ti-stripe 7 m wide along the X-axis on the -c side of a 0.5 mm thick, 4 ”Z-cut LiNbO ₃ wafer. Diffusion at 1060 ℃ for a time to produce a channel waveguide. After removing the thin domain inversion layer of the + c plane generated during Ti diffusion, the polarization direction of LiNbO ₃ is reversed to place the Ti waveguide on the + c plane, followed by a periodic photoresist pattern and liquid electrode technology ( Periodic polarization is made using the liquid electric technique. In general, the voltage and spontaneous polarization required for polarization reversal are around 21 kV / mm and 78 μC / cm ² , respectively. Finally, stress generated during the induction of electrical polarization is removed by annealing. Recent advances in polarization reversal technology have boosted the second harmonic efficiency of Ti: PPLN waveguide devices to thousands of percent / W. Ti waveguides generally have a cross-sectional area of 4x5 μm ² and losses of less than -5 dB when coupled using optical fibers.

The fabrication of the conventional annealed proton exchange (APE) and titanium (Ti: titanium) diffusion PPLN waveguides has a problem in that the process is complicated and the production of three-dimensional devices is difficult.

An object of the present invention for solving the above problems is to provide a manufacturing method capable of manufacturing a PPLN waveguide device using an ultra-short pulse laser.

The present invention for achieving the above object, the step of generating an ultra-short pulse laser; And irradiating the ultra-short pulsed laser into the PPLN to induce a change in refractive index to form a waveguide, but generating a second harmonic wave using the waveguide device on the PPLN. To provide.

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

Example

1 is a block diagram showing an example of a PPLN waveguide device manufacturing apparatus using a laser according to a preferred embodiment of the present invention.

Referring to FIG. 1, the PPLN waveguide device manufacturing apparatus includes a laser light source 100, a beam transmission system 120, a beam splitter 140, a light collector 160, and a driving stage 180.

The laser light source 100 preferably uses an ultra-short pulse laser. In the present invention, a femtosecond laser having a specification of 785 nm, 1 W, 184 fs, and 1 kHz is used for the laser light source 100.

The pulse laser generated from the laser light source 100 is incident to the beam transmission system 120. The beam transmission system 120 has optical systems and devices for controlling the pulse laser.

The pulse laser beam passing through the beam transmission system 120 is incident to the beam splitter 140. The beam splitter 140 reflects the incident pulse laser to the light collector 160, and transmits visible light so that the camera 210 can check the processing state of the film 200.

The collector 160 collects the pulsed laser beam incident from the beam splitter 140 and irradiates the pulsed laser beam into the PPLN 200, which is a workpiece.

When the pulse laser is irradiated from the light collector 160 onto the film 200, the stage 180 performs a continuous moving operation. The PPLN waveguide is continuously formed by the movement of the stage 180. That is, a three-dimensional waveguide can be formed inside the PPLN by inducing a refractive index change by irradiating an ultra-short pulse laser. Therefore, when continuously irradiating the ultra-short pulse laser and moving the stage 180 at a constant speed, a waveguide having a constant size is formed inside the PPLN 200 which is a workpiece.

2 is a measurement photograph of a PPLN waveguide device according to a preferred embodiment of the present invention.

Referring to FIG. 2, a femtosecond laser (1 kHz, 184 fs, 0.5 mJ @ 785 nm) beam is focused on a 20 times objective lens (0.4 NA) at a feed rate of 20 um / s of the stage in FIG. 1. A waveguide with a width of 4.7 um was formed at a depth of 20 um on the PPLN surface. The waveguide element was 44.8 mm long and the total waveguide loss was -12.9 dB at TM polarization at 1550 nm. The mode size of the waveguide was also measured to be 11.7 μm × 8.7 μm (FWHM).

In the present invention, the amount of change in the refractive index of the waveguide formed inside the PPLN may be controlled by adjusting the pulse intensity of the laser light source. In addition, the width of the waveguide can be controlled by superimposing the waveguides at regular intervals. As described above, when the PPLN waveguide device is manufactured using the ultra-short pulse laser of the present invention, the processing conditions such as the intensity of the laser, the size of the beam, and the focal length may be adjusted to adjust the amount and shape of the refractive index change of the waveguide.

3 is a second harmonic wave generation experiment apparatus using the PPLN waveguide device manufactured by the ultra-short pulse laser.

The output and wavelength of the external resonator laser 400 were controlled by the computer 410, where the polarization of the beam incident on the sample was the secondary nonlinear coefficient d ₃₃ of lithium naobate (LN). In order to maximize the effect of the TM polarized light (420) was fixed. The generated second harmonic wave was measured using a 10-fold objective lens 430 and a silicon detector 440.

4 is a second harmonic curve measured by varying the wavelength of the external resonator laser 400 in the second harmonic wave generation experiment apparatus of FIG.

The full width at half maximum (FWHM) of the second harmonic wave was about 0.25 nm, indicating that this narrow bandwidth occurred throughout the length of the PPLN waveguide. In the PPLN waveguide device fabricated with a femtosecond laser, as shown in FIG. 4, a second harmonic wave is generated in the 1560 nm band.

The second harmonic wave generated in the PPLN waveguide device is an important parameter to know whether the PPLN waveguide device has nonlinear characteristics. That is, when the second harmonic wave is generated, it can be seen that the PPLN waveguide device has a desired nonlinear characteristic, and when the magnitude of the second harmonic wave is large, the PPLN waveguide device has a good nonlinear characteristic.

According to the present invention, a PPLN waveguide device is formed by using an ultra-short pulse laser. In addition, the amount of change in the refractive index of the waveguide formed inside the PPLN may be controlled by adjusting the pulse intensity of the laser light source. Therefore, the PPLN waveguide device can be easily formed.

According to the present invention as described above, a PPLN waveguide having a nonlinear characteristic can form a waveguide inside the PPLN using an ultra-short pulse laser. Therefore, it is possible to fabricate the nonlinear PPLN waveguide device in a very simple method compared to the conventional method.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (3)

Generating a femtosecond laser which is an ultra-short pulse laser; And Irradiating the femtosecond laser inside the PPLN to induce a change in refractive index to form a waveguide, Generating a second harmonic wave using a waveguide element in the PPLN; The method of manufacturing a PPLN waveguide device, characterized in that for controlling the width of the waveguide by overlapping the waveguide at a predetermined interval. The method of claim 1, wherein the refractive index of the waveguide formed inside the PPLN is controlled by adjusting a pulse intensity of the femtosecond laser. delete

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