JPH04172427A - Light wave length converting element and short wave length laser light source - Google Patents

Abstract

PURPOSE:To stably generate higher harmonic waves and greatly enhance stability in the output of the higher harmonic waves by using both a poralization inversion layer which consists of at least more than two portions of different periods and a semiconductor laser light source which is driven at high frequencies. CONSTITUTION:SiO2 6 is patterned on a LiNbO3 base 1 using a normal photographing process and dry etching. The LiNbO3 base on which the SiO2 is formed is then subjected to heat treatment at 1080 deg.C for 90 minutes to form a poralization inversion layer 3 of thickness 1.4 mum just below the SiO2 6. Further, the base 1 is etched with a 1:1 mixed solution of HF and HNF3 for 20 minutes to remove the SiO3 6 and a light wave guide passage 2 is formed in the poralization inversion layer 3 using proton exchange method. Fundamental wave P1 entering the light wave guide passage 2 is converted to higher harmonic waves P2 at the poralization inversion layer and the power of the higher harmonic waves is increased at the next non-poralization inversion layer. The waves P2 the power of which has thus been increased inside the passage 2 are radiated from a radiating portion 12. Even though the degree of allowance of this higher harmonic waves output at a portion corresponding to its period A alone is as small as a half band width DELTAlambda, the waves are added together at portions corresponding to periods A, B, C, D whereby the half band width DELTAlambda is enlarged four times.

Description

Detailed Description of the Invention Industrial Field of Application The present invention relates to optical wavelength conversion elements and short wavelength laser light sources used in the field of optical information processing using coherent light or the field of optical measurement and control. Technical Figure 7 shows the configuration diagram of a conventional optical wavelength conversion element.
Harmonic generation for the fundamental wave with a wavelength of 0.6 μm (wavelength 0.06 μm)
53 μm) using figures; 5. (
E., J., Lim, M.I.M., Fejer, R.L., B.
yer, 'Secondharmonic gen
generation of blue and green
lightin periodically-pol
ed planar lithium niobate
waveguides', I G W 0. 19
88L), LiNbO as shown in FIG.
5. An optical waveguide 2 is formed on the substrate 5, and a layer 3 (poling inversion layer) whose polarization is periodically inverted is formed on the optical waveguide 2. By compensating with the periodic structure of the inversion layer 3, it is possible to output harmonics with high efficiency. When the fundamental wave P1 is incident on the incident surface 10 of the optical waveguide 2, the harmonic wave P2 is efficiently generated from the optical waveguide 2. Conventional optical wavelength conversion elements such as this, which operate as wavelength conversion elements, have a polarization inversion structure as their basic component.
Although it is explained using a diagram, the same F! i! In J(a), a pattern of Ti31 is formed on the LiNbO5 substrate 1, which is a nonlinear optical crystal, with a period of several μm in width by lift-off and vapor deposition.9 Next, as shown in FIG. Next, a polarization inversion layer 3 whose polarization was inverted in the opposite direction to that of the substrate 1 was formed.
After performing heat treatment for 30 minutes at 0°C, annealing was performed at 350°C to form the optical waveguide 2. When the length of the optical waveguide is 1 mm and the power of the fundamental 4pi is 1rn, W, the power of harmonic P2 is 0.
If 5nW is obtained, and the fundamental wave is 40mW, a harmonic output of 800nW is possible.In this case, 1
The conversion efficiency per IW in a cm device is 5%/W-cm.

Problems to be Solved by the Invention In an optical wavelength conversion element based on a polarization inversion layer as described above, when the element length is 5 mm, the tolerance to the laser wavelength is narrow and the half width is 0.8 nm or u%.Therefore, the optical wavelength conversion element When combined with a semiconductor laser, there is a problem that the semiconductor laser will fluctuate in wavelength due to temperature changes, resulting in no harmonics being produced or the harmonic output fluctuating significantly.Specifically, if the semiconductor laser changes in temperature by 1℃ As a result, the wavelength changes by 0.3 nm, and a change of 3 degrees Celsius causes the output to disappear. By adding new ideas to the element, we provide an optical wavelength conversion element that stably outputs harmonics even when the temperature changes in a semiconductor laser.
The present invention has a polarization inversion layer and an optical waveguide in a nonlinear optical crystal, and the polarization inversion layer has at least two different periods.
In order to obtain stable output, the short wavelength laser light source of the present invention includes an optical wavelength conversion element having a polarization inversion layer and an optical waveguide in a nonlinear optical crystal, and a semiconductor laser. In addition, the semiconductor laser is driven at a high frequency.The optical wavelength conversion element of the present invention improves the tolerance to wavelength and provides stable harmonic generation. According to a short wavelength laser light source, the output stability of harmonics can be greatly improved by widening the spectrum of the semiconductor laser by high-frequency driving. First, FIG. 1 shows a structural diagram of a first embodiment of an optical wavelength conversion element according to the present invention. In this example, an optical waveguide 2 fabricated using proton exchange in a LiNbO3 substrate 1 is used as a polarization inversion type optical wavelength conversion element. 2 is the formed optical waveguide wide 10 is the incident plate for the fundamental wave P1, and 12 is the output part for the harmonic P2.This optical waveguide 2 has polarization with different periods. Periodic structure with inversion layer B, C, D
is formed.a The fundamental wave P1 entering the optical waveguide 2 is converted into a harmonic wave P2 by a polarization inversion layer having a length equal to the phase matching length, and is converted into a harmonic wave P2 by the next non-polation inversion layer having a length of L. The harmonic power will increase.

In this way, the harmonic wave P whose power is increased within the optical waveguide 2
2 is radiated from the emission part 12, and the harmonics (SH
G) Shows the wavelength dependence of the output. The tolerance only for the period A part is small, half-width △λ, but to the period B, C, D 4
The half-width △λ is expanded by four times.The method for manufacturing this optical wavelength conversion element will be explained using diagrams.
Patterning 5iOa 6 on 0a substrate 1 using normal photo process and dry etching Periodic structure iA
The periods of ~D are 3,000 μra, 3.001 μm, 3.002 μm, and 3.003 μm, respectively, and the periods are determined so that they overlap at the point where the harmonic output drops to half.Next, as shown in the same figure (b), SiO2 is formed. st'L taLi
NbO5 substrate 11. : 1080t, heat treated for 90 minutes to form a 1.5mm thick layer directly under the SiO26. The rate of increase in heat treatment to form the polarization inversion layer 3 of 4 μm is 10°C/trip.
Even if the cooling rate is 50℃/min, if the cooling rate is slow, uneven reversal will occur, so a cooling rate of 30℃/min or more is desirable.
Immediately below ins 6, Li decreases and the Curie temperature decreases, so polarization can be partially inverted.The length L of the polarization inversion layer 3 is 1.5 μm.Next, in the same figure (C), HF:
Etch for 20 minutes with a 1=1 mixture of HNFs5.
Next, the optical waveguide 2 is formed in the polarization inversion layer 3 using proton exchange. After patterning Ta2Og in a stripe shape as a mask for the optical waveguide 2, a Ta206 mask with a width of 6 μm is formed. length 25mm
230t with slits formed.

Proton exchange was performed for 2 minutes.Finally, the mask was removed and annealing was performed at 350°C for 1 hour.The annealing treatment made the layer uniform, reduced loss, and returned nonlinearity to the proton exchange layer. The area directly under the slit of the protective mask where protons have been exchanged has a refractive index of 0. The light propagates through the high refractive index layer 2, which has been raised by about O3, and this becomes the optical waveguide 2.The optical waveguide is manufactured by the process described above.The thickness d of the optical waveguide 2 is 1 .2 μm, which is smaller than the 1.4 μm thickness of the polarization inversion layer 3, and the wavelength can be effectively converted.
There is no change in the refractive index of the non-poled layer 4 and the polarized layer 3 of this optical waveguide 2, and the propagation loss when light is guided is small.

A surface perpendicular to the optical waveguide 2 is optically polished to form an entrance section 10 and an exit section 12. In this manner, the optical wavelength conversion element shown in FIG. 1 can be manufactured. In addition, the length of this element is 20 mm. In Fig. 1, when semiconductor laser light (wavelength 0.84 μm) is guided from the incident part 10 as the fundamental wave P1, a single mode propagates as a harmonic P2 with a wavelength of 0.42 μm. The propagation loss of the optical waveguide 2 is as small as 1 dB/cm, and the harmonic P2 is effectively extracted.9 One of the reasons for the low loss is that a uniform optical waveguide is formed using phosphoric acid. Itatamo Fundamental Wave 4
Obtaining 1 mW harmonic (wavelength 0.42 μm) with 0 mW input. Even though the conversion efficiency is 2.5% in this case, the wavelength tolerance is significantly improved to 3.2 nm compared to the conventional 0.8 nm. The semiconductor laser can stably obtain harmonic output even when the temperature changes by about 10°C.In contrast to the fundamental wave, the harmonic output is unstable in multimode propagation and is not practical. If the period of the polarization inversion layer is made up of four or more different parts, it is possible to generate harmonics against the normal fluctuations of the semiconductor laser, which is particularly effective. After confirming harmonic generation by the present optical wavelength conversion element using the fundamental wave, a second embodiment of the short wavelength laser light source of the present invention will be described. A block diagram of the short wavelength laser light source of FIG. 4 is shown. A short wavelength laser light source basically consists of a semiconductor laser 21, an optical wavelength conversion element 22, and a high frequency power source 23.
The fundamental wave P1 emitted from the semiconductor laser 2I fixed to the frame 20 is made into parallel light by the collimator lens 24, and then
The focus lens 25 introduces the light into the optical waveguide 2 of the light wavelength conversion element 22 and converts it into a harmonic P2, but the structure of the light wavelength conversion element is the same as that in the first embodiment.
In this example, M
GO-doped LLNbO3 is heat-treated at 1100℃ to form a polarization inversion layer. In this example, a short wavelength laser light source was fabricated by combining this optical wavelength conversion element and a semiconductor laser. Frequency 1. The spectrum of the semiconductor laser 21 is broadened by driving the wavelength laser light source at a high frequency using a high frequency power supply 23. GHz and a high frequency output of 2 W. Figure 5 shows the spectrum spread of a semiconductor laser. Before high-frequency driving, it was a single vector of less than 0.1 nm, but after driving it became a multispectrum and expanded to 4n, m. This further improves wavelength tolerance4
The driving frequency is IGH2 and the repetition is fast, so it is no different from continuous light.The tolerance of the optical wavelength conversion element is 0.8 nm.
In this case, a decrease in harmonic output becomes a problem.

However, this problem does not occur because the peak output of the semiconductor laser is improved by high-frequency driving. Figure 6 shows the time waveform of the semiconductor laser in the case of high-frequency driving. The semiconductor laser has an average output of 4.0 mW, a peak output of 1 W, and a pulse width of 30 ps.

Since the conversion efficiency to harmonics increases in proportion to the fundamental wave output, the average conversion efficiency also improves. The conversion efficiency is 2% with 40 mW manual power, and the a-power is very stable over a range of about 14° C. A third embodiment of the optical wavelength conversion element of the present invention will be described below. The configuration of the optical wavelength conversion element is the same as in the embodiment. In this example, 1.1Ta, Os is used instead of the LiNbO5 substrate.
was used as a substrate, and the period was divided into 5. Specifically, 4 μm, 4.001 μm, 4. 002μrn
,4. 003μrrK 4. 4 The Curie temperature of LiTaO3 is as low as 630°C, and polarization inversion processing can be performed at low temperatures.4 The thickness of the optical waveguide 2 is 1.5 μm, and the length is 2 crn [, 1 Taos].
Since the optical waveguide fabricated on the substrate 1a by proton exchange has large nonlinearity, it is not necessary to perform annealing treatment.

The conversion efficiency in this example is 1% at 40mW input,
The wavelength tolerance is 4 nm, and L i, T a O3
Since it uses LiNb0a and L as nonlinear optical crystals, there is no optical damage and the harmonic output is very stable.
Although iTa0a was used, ferroelectric E such as KNbOs and KTP was used.
It is also applicable to organic materials such as MNA.

As described in detail of the invention, the optical wavelength conversion element of the present invention and the short wavelength 1/-the light source form polarization inversion layers with different periods of ζA, thereby significantly increasing the Moreover, according to the short wavelength laser light source of the present invention, by driving the semiconductor laser at high frequency, the wavelength spectrum of the semiconductor laser can be expanded, and the tolerance can be greatly expanded, and stable operation can be realized. .

Furthermore, by using the optical wavelength conversion element of the present invention, harmonics can be taken out from the optical waveguide, and a spot without astigmatism can be easily obtained, and its practical effect is extremely large.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of the first embodiment of the optical wavelength conversion element of the present invention. Fig. 2 is a graph showing the tolerance of the optical wavelength conversion element of the present invention. Fig. 3 is the optical wavelength of the first embodiment. Figure 4 shows the manufacturing process of the conversion element of the present invention. Figure 7 shows the structure of the conventional optical wavelength conversion element. Figure 8 shows the manufacturing process of the conventional optical wavelength conversion element. ...Optical waveguide 3...Polarization inversion layer pi...Fundamental wave, P2...
Name of Kocho Watari agent: Patent attorney Akira Kokaji and 2 others 1
--- Li Nb0a basis interpretation 2-m-Light 1 wave 1 trough A-o- turbidity (l″l5) 1-L-mountain b03gure 2-, -light S1 picture- Fig. 7 3-Kai Hiru 1st layer Fig. 8 cQ) 37 (by) 3

Claims (1)

Claims: (1) An optical wavelength conversion element having a polarization inversion layer and an optical waveguide in a nonlinear optical crystal, and characterized in that the polarization inversion layer consists of at least two or more parts with different periods. (2) A short wavelength laser light source comprising a semiconductor laser and an optical wavelength conversion element having a polarization inversion layer and an optical waveguide in a nonlinear optical crystal, the semiconductor laser being driven at a high frequency. (3) Nonlinear optical crystal is LiNb_xTa_
1_-_xO_3 (0≦X≦1) The optical wavelength conversion element according to claim (1) or the short wavelength laser light source according to claim (2), characterized in that the substrate is a 1_−_xO_3 (0≦X≦1) substrate. (4) The optical wavelength conversion element according to claim (1) or the short wavelength laser light source according to claim (2), wherein the optical waveguide is a proton exchange optical waveguide. (5) The optical wavelength conversion element according to claim (1), which has a polarization inversion layer having four or more different periods. (6) Claim No. 1, characterized in that the optical waveguide has single mode propagation for semiconductor laser light.
The optical wavelength conversion element described in .