- Email: [email protected]
Flux growth of large potassium titanyl phosphate crystals and their electro-optical applications
Journal of Crystal Growth 237–239 (2002) 672–676
Flux growth of large potassium titanyl phosphate crystals and their electro-optical applications Xiaoyang Wang, Xin Yuan, Wei Li, Jiabao Qi, Shengjun Wang, Dezhong Shen* Research Institute of Synthetic Crystals, P.O. Box 733, Beijing 100018, China
Abstract In this paper, an improved top-seeded solution growth has been developed. Potassium titanyl phosphate (KTiOPO4 or KTP) crystals with the size 60 60 50 mm3 were grown from K6P4O13 flux by this method, from the as-grown crystals big Z-cut crosssection (60 60 mm2) could be attained, which would be advantageous to the electro-optical (E-O) applications of KTP crystals. The tests of E-O modulation by flux KTP has been realized, compared with LiNbO3 and KD*P, the results showed that E-O modulator formed by flux KTP is free from acoustic ringing, and can modulate at subnanosecond level. All this indicated that KTP is an attractive material for various E-O applications, especially as an E-O Q-switch device in a high-repetition-rate, high-speed-traveling wave laser system. r 2002 Published by Elsevier Science B.V. PACS: 07.60; 42.70; 77.84 Keywords: A2. Top seeded solution growth; B1. Phosphates; B1. Potassium compounds; B2. Nonlinear optic materials
1. Introduction Potassium titanyl phosphate (KTP) has been shown to have superior properties for several nonlinear optical applications and in particular, for doubling the frequency of 1064 nm radiation of Nd:YAG lasers. Its high nonlinear-optical coefficients, high optical damage threshold, wide acceptance angles, and thermally stable phase-matching properties make it suitable for this purpose. In addition to having attractive nonlinear-optical characteristics, KTP has large linear electrooptical (E-O) coefficients and low dielectric constants [1], which makes it attractive for various *Corresponding author. E-mail address: [email protected] (D. Shen).
electro-optical applications, such as modulators and Q switches. KTP also has an electro-optical waveguide modulator figure of merit that is nearly double that of any other inorganic material, this suggests that KTP is also promising for integratedoptical applications [2]. KTP decomposes before 11501C, and hence normal melt processes cannot be used to grow this material. The techniques presently used to grow KTP crystals include the hydrothermal and flux method, the former process is similar to quartz crystal growth except for the higher temperatures (of the order of 5001C) and pressures (of the order of 1360 bar) needed for KTP [3,4]. For the sake of the restrictions of equipment, the KTP crystal size is limited to an approximately small magnitude, with a seed in the middle of the crystals. In a word,
0022-0248/02/$ - see front matter r 2002 Published by Elsevier Science B.V. PII: S 0 0 2 2 - 0 2 4 8 ( 0 1 ) 0 1 9 9 1 - 1
X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
hydrothermal technique needs rigorous apparatus and conditions, and it is very difficult to exploit on an industrial scale, which is due to some technical problems. However, large single crystals of KTP can mainly be grown by flux techniques, the significant advantage of using the flux process is that it operates at atmospheric pressure and hence does not require sophisticated pressure equipment, the crystals can be grown at atmospheric pressure and it is easy to design scaled-up furnaces. There are many reports on the growth and quality of KTP crystals [5–7], typical crystal sizes obtained are about several centimeters long. However, KTP crystals grown by the normal flux method can hardly get a big Z-cut crosssection because of the very slow growth rate in the xðaÞ direction. This does not help the E-O applications of KTP crystals, for most KTP samples used in E-O applications are taken from the Z-cut plane. In this paper, we report on the flux growth and E-O applications of large KTP crystals. Crystals with the size 60 60 50 mm3 and big Z-cut crosssection were grown from K6P4O13 (K6) using an improved top-seeded method, the results of their E-O application are also discussed.
2. Crystal growth The flux technique is essentially a high-temperature solution-growth process in which the KTP crystallizes out of a molten KTP/flux composition when cooled. Common fluxes used are various potassium phosphates, with the K:P ratio varying from 1 to 3. However, to avoid growth striations and flux inclusions, uniform temperatures and high level of temperature control are required. To obtain these conditions, well-insulated furnaces and heat pipes have been used. We used a vertical cylindrical electric furnace with an inner diameter of 320 mm and a height of 900 mm. The heater elements were divided into five zones and controlled individually in order to obtain satisfactory temperature distributions. A platinum crucible, 270 mm in diameter and 270 mm in height was located at the center of the
673
furnace. In this system, the temperature difference of the solution in the crucible between the top part and the bottom part was o51C. K6P4O13 (K6) was used as a flux. The starting materials were prepared by dehydration of the mixture of K2HPO4, KH2PO4 and TiO2 powder. The amount of charged material in the crucible was approximately 25 kg in weight. The saturation temperature of the starting solution was approximately 8501C. After sufficient stirring, using a platinum stirrer, improved top-seeded solution growth (ITSSG) was carried out using a seed of several centimeters long. The seed was rotated at 15 rpm and the direction of the rotation was inverted every 300 s, this will be very useful to transport solute to reach the seed. The solution temperature was reduced in accordance with a set procedure. A crystal with a dimension of 60 60 50 mm3 (150 g in weight) was obtained. The KTP crystal morphology is similar for various potassium phosphates fluxes, and the specifics depend on seed size and orientation. It is noticeable that when we use a typical flux, such as K5 and K6, the growth rate in xðaÞ direction is very low compared with other directions, so the asgrown crystal always has a small dimension in the xðaÞ direction, which does hardly exceed 40 mm; that is to say, the Z-cut crosssection of as-grown KTP is not large enough because of the restriction in the xðaÞ direction. This is disadvantageous to the E-O application of KTP, for KTP samples used in E-O applications are mostly taken from Z-cut plane. To overcome this shortcoming, we developed ITSSG, the key point is to ‘‘breed’’ a long seed in the (1 0 0) direction. After many periods of growth, the seed may have a long side more than 55 mm along the xðaÞ direction. When we induct the long seed, we keep the long side of the seed close to the liquid surface, the growth will take place along the whole long side, thus the asgrown crystal has enough length in the xðaÞ direction, despite its very slow growth rate in this direction. Finally, we obtain large crystals of KTP with big Z-cut crosssection, as shown in Fig. 1. Using ITSSG, we can make the length in the xðaÞ direction of KTP crystals exceed 60 mm, furthermore, after enough growth cycles, it can even exceed 70, 80 mm, and so on.
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X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
above-mentioned aspect, the reduction of temperature is usually not a constant. 3. E-O applications of KTP
Fig. 1. As-grown KTP crystals with big Z-cut crosssection by the ITSSG method.
Although there are many reports on the E-O applications of KTP crystals [8–10], the samples used were mostly grown by the hydrothermal technique. We have carried out some experiments for the E-O applications of the KTP; all the KTP samples used in these experiments were grown by the flux method. 3.1. KTP E-O waveguide
To grow high-quality KTP crystals without any liquid inclusion, the set procedure of lowering temperature is very important besides other growth parameters. We set the procedure of lowering temperature according to two factors, the first is the area of the total growth surfaces which can ‘‘accept’’ the growth unit. Obviously, great area means a great ability to ‘‘accept’’ the growth unit, and it means ability of growth, so we can lower the temperature relatively fast; the second factor is the effect of stirring. The procedure of lowering the temperature is mainly set according to the first factor, but is adjusted in the middle of the growth period by the second factor. We consider the different stages during the period of crystal growth, at first, the stirring of the solution is not enough because the crystal is too small, when compared with the volume of the solution; therefore, only the solute in the supersaturated solution near the crystal can reach the growth surface. So the growth rate is relatively low. Next, as the crystal becomes larger, the stirring effect of solution by the crystal becomes larger. The stirred region may extend to much of the solution, then the solute far from the crystal approaches the growing surface. In this stage, the growth rate becomes very high, at this time, we usually reduce the lowing rate of temperature, even maintain the temperature as a constant. Finally, when the solute for the excess supersaturation has been spent, the growth rate becomes stable and corresponds to the cooling rate of the temperature. Considering the
Optical waveguides have been fabricated on the flux KTP substrate with the size 20 10 3 mm3 by using an ion-exchange process that is similar to that used in forming waveguides in the glass substrate, the waveguides formed in this way have an exchange-ion concentration depth profile and refractive-index profile, that is close to a complementary error-function distribution, device thermal stability is much better. 3.2. KTP E-O modulator KTP is a biaxial crystal with an orthorhombic structure (point group mm2). The crystallographic directions a, b, c correspond to the optic axes x, y, z, with c being the polar axis. When used in amplitude modulation, as per calculation, it is required that the KTP crystal be cut normal to the principal crystal axes, the direction of lightwave propagation coincides with the y-axis, and the electric field coincides with the z-axis. From consideration of KTP’s mm2 point symmetry, light-amplitude modulation for a beam propagating along the y-axis requires the beam to be polarized 451 relative to the x-axis with the electric field along the z (polar axis)-direction. It is important to note that the KTP crystal has in fact an arbitrary static birefringence, and it has to be compensated for. For the sake of convenience, we use a couple of bulk KTP crystals with the same dimensions, one bulk turned 901 to the other, to compensate for the static birefringence, just as shown in Fig. 2.
X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
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Fig. 2. A couple of bulk KTP crystals with the same dimensions, the one bulk turned 901 to the other, to compensate for the static birefringence.
3.2.1. Compared with LiNbO3 Q-switch was formed by a couple of KTP crystals with the size 4 16 4 mm3. The y-faces were optically polished and Ar-coated, and the ( electrodes were deposited on the z-faces with 500 A of sputtered gold. We use a high-voltage pulse generator with 1 KHz repetition frequency as a driver, under the condition of switching pulsewidth of 120–1200 ns and leading and trailing edges of 5 ns, to modulate the light beam of CW Ti:Al2O3 laser with 800 nm wavelength. The test results displayed regular rectangular optical pulse figuration without any acoustic ringing, as shown in Fig. 3. The half-wave voltage is about 580 V. In the same condition, except for replacing the two KTP crystals by a piece of LiNbO3 crystal with the same dimensions (4 16 4 mm3), we can see a strong acoustic ringing, as shown in Fig. 4. The half-wave voltage is about 1800 V. Considering that the total length of two KTP crystals is twice that of one LiNbO3 crystal, we can say the dynamic half-wave voltage of KTP is about 30–40% less than that of LiNbO3. The dynamic half-wave voltage is the important criterion for Q-switch applications. Moreover, KTP has almost no acoustic ringing, which is just the drawback of LiNbO3 crystal. 3.2.2. Compared with KD*P Bulk high-speed traveling wave E-O modulator was also fabricated using a couple of KTP crystals with the size 4 8 16 mm3, the half-wave voltage is just 760 V, response time of the device is low up to 297 ps. By contrast, E-O modulator fabricated by the KD*P crystal usually has a half-wave voltage of 7–8 kV and, in addition, a large
Fig. 3. The oscillograph of switching a CW laserbeam of KTP crystals, regular optical pulse figuration can be seen.
Fig. 4. Replaced KTP of the same device used in Fig. 3 by LiNbO3, some higher-order acoustic oscillations during the pulse can be observed.
distributing capacity of the device because KD*P’s dielectric is as large as 40, thus the device has a very slow response speed and cannot be modulated at the subnanosecond level.
4. Conclusions From our work, we have developed an improved top-seeded solution growth. Using this method, we obtained KTP crystals with the size
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X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
60 60 50 mm3 which can obtain big Z-cut crosssection from as-grown crystals, this will be advantageous to cutting for its E-O application. We have also carried out some experiments for E-O applications using flux KTP crystals, and the results showed, based on both low half-wave voltage and lack of piezoelectric-induced parasitics, that KTP has promising potential for various E-O modulation applications other than its major role as a doubling crystal. However, KTP crystals by the flux technique have a lower production cost, this makes us see the possibility of its large-scale application. Our work has shown low-cost flux KTP to be a strong candidate for the E-O applications.
Acknowledgements We acknowledge the valuable contributions of Mr. Li Shicheng, Sui Zhan et al., for device
preparation, E-O experiments and for their other support and encouragement.
References [1] J.D. Bierlein, C.B. Arweiler, Appl. Phys. Lett. 49 (1986) 917. [2] J.D. Bierlein, A. Ferretti, L.H. Brixner, W.Y. Hsu, Appl. Phys. Lett. 50 (1987) 1216. [3] J.D. Bierlein, H. Vanherzeele, J. Opt. Soc. Am. B6 (1989) 622. [4] R.A. Laudise, R.J. Cava, A.J. Caporaso, J. Crystal Growth 74 (1986) 275. [5] P.F. Bordui, J.C. Jacco, G.M. Loiacono, R.A. Stolzenberger, et al., J. Crystal Growth 84 (1987) 403. [6] R.J. Bolt, H. de Haas, M.T. Sebastian, H. Klapper, J. Crystal Growth 110 (1991) 587. [7] P.J. Halfpenny, L.O. Neill, J.N. Sherwood, G.S. Simpson, et al., J. Crystal Growth 113 (1991) 722. [8] X.D. Wang, P. Basseras, R.J. Dwayne Miller, H. Vankerzeele, Appl. Phys. Lett. 59 (1991) 519. [9] Takunori Taira, Takao Kobayashi, IEEE J. Quantum Electron. 30 (1994) 800. [10] C.A. Ebbers, S.P. Velsko, Appl. Phys. Lett. 67 (1995) 593.
Flux growth of large potassium titanyl phosphate crystals and their electro-optical applications Xiaoyang Wang, Xin Yuan, Wei Li, Jiabao Qi, Shengjun Wang, Dezhong Shen* Research Institute of Synthetic Crystals, P.O. Box 733, Beijing 100018, China
Abstract In this paper, an improved top-seeded solution growth has been developed. Potassium titanyl phosphate (KTiOPO4 or KTP) crystals with the size 60 60 50 mm3 were grown from K6P4O13 flux by this method, from the as-grown crystals big Z-cut crosssection (60 60 mm2) could be attained, which would be advantageous to the electro-optical (E-O) applications of KTP crystals. The tests of E-O modulation by flux KTP has been realized, compared with LiNbO3 and KD*P, the results showed that E-O modulator formed by flux KTP is free from acoustic ringing, and can modulate at subnanosecond level. All this indicated that KTP is an attractive material for various E-O applications, especially as an E-O Q-switch device in a high-repetition-rate, high-speed-traveling wave laser system. r 2002 Published by Elsevier Science B.V. PACS: 07.60; 42.70; 77.84 Keywords: A2. Top seeded solution growth; B1. Phosphates; B1. Potassium compounds; B2. Nonlinear optic materials
1. Introduction Potassium titanyl phosphate (KTP) has been shown to have superior properties for several nonlinear optical applications and in particular, for doubling the frequency of 1064 nm radiation of Nd:YAG lasers. Its high nonlinear-optical coefficients, high optical damage threshold, wide acceptance angles, and thermally stable phase-matching properties make it suitable for this purpose. In addition to having attractive nonlinear-optical characteristics, KTP has large linear electrooptical (E-O) coefficients and low dielectric constants [1], which makes it attractive for various *Corresponding author. E-mail address: [email protected] (D. Shen).
electro-optical applications, such as modulators and Q switches. KTP also has an electro-optical waveguide modulator figure of merit that is nearly double that of any other inorganic material, this suggests that KTP is also promising for integratedoptical applications [2]. KTP decomposes before 11501C, and hence normal melt processes cannot be used to grow this material. The techniques presently used to grow KTP crystals include the hydrothermal and flux method, the former process is similar to quartz crystal growth except for the higher temperatures (of the order of 5001C) and pressures (of the order of 1360 bar) needed for KTP [3,4]. For the sake of the restrictions of equipment, the KTP crystal size is limited to an approximately small magnitude, with a seed in the middle of the crystals. In a word,
0022-0248/02/$ - see front matter r 2002 Published by Elsevier Science B.V. PII: S 0 0 2 2 - 0 2 4 8 ( 0 1 ) 0 1 9 9 1 - 1
X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
hydrothermal technique needs rigorous apparatus and conditions, and it is very difficult to exploit on an industrial scale, which is due to some technical problems. However, large single crystals of KTP can mainly be grown by flux techniques, the significant advantage of using the flux process is that it operates at atmospheric pressure and hence does not require sophisticated pressure equipment, the crystals can be grown at atmospheric pressure and it is easy to design scaled-up furnaces. There are many reports on the growth and quality of KTP crystals [5–7], typical crystal sizes obtained are about several centimeters long. However, KTP crystals grown by the normal flux method can hardly get a big Z-cut crosssection because of the very slow growth rate in the xðaÞ direction. This does not help the E-O applications of KTP crystals, for most KTP samples used in E-O applications are taken from the Z-cut plane. In this paper, we report on the flux growth and E-O applications of large KTP crystals. Crystals with the size 60 60 50 mm3 and big Z-cut crosssection were grown from K6P4O13 (K6) using an improved top-seeded method, the results of their E-O application are also discussed.
2. Crystal growth The flux technique is essentially a high-temperature solution-growth process in which the KTP crystallizes out of a molten KTP/flux composition when cooled. Common fluxes used are various potassium phosphates, with the K:P ratio varying from 1 to 3. However, to avoid growth striations and flux inclusions, uniform temperatures and high level of temperature control are required. To obtain these conditions, well-insulated furnaces and heat pipes have been used. We used a vertical cylindrical electric furnace with an inner diameter of 320 mm and a height of 900 mm. The heater elements were divided into five zones and controlled individually in order to obtain satisfactory temperature distributions. A platinum crucible, 270 mm in diameter and 270 mm in height was located at the center of the
673
furnace. In this system, the temperature difference of the solution in the crucible between the top part and the bottom part was o51C. K6P4O13 (K6) was used as a flux. The starting materials were prepared by dehydration of the mixture of K2HPO4, KH2PO4 and TiO2 powder. The amount of charged material in the crucible was approximately 25 kg in weight. The saturation temperature of the starting solution was approximately 8501C. After sufficient stirring, using a platinum stirrer, improved top-seeded solution growth (ITSSG) was carried out using a seed of several centimeters long. The seed was rotated at 15 rpm and the direction of the rotation was inverted every 300 s, this will be very useful to transport solute to reach the seed. The solution temperature was reduced in accordance with a set procedure. A crystal with a dimension of 60 60 50 mm3 (150 g in weight) was obtained. The KTP crystal morphology is similar for various potassium phosphates fluxes, and the specifics depend on seed size and orientation. It is noticeable that when we use a typical flux, such as K5 and K6, the growth rate in xðaÞ direction is very low compared with other directions, so the asgrown crystal always has a small dimension in the xðaÞ direction, which does hardly exceed 40 mm; that is to say, the Z-cut crosssection of as-grown KTP is not large enough because of the restriction in the xðaÞ direction. This is disadvantageous to the E-O application of KTP, for KTP samples used in E-O applications are mostly taken from Z-cut plane. To overcome this shortcoming, we developed ITSSG, the key point is to ‘‘breed’’ a long seed in the (1 0 0) direction. After many periods of growth, the seed may have a long side more than 55 mm along the xðaÞ direction. When we induct the long seed, we keep the long side of the seed close to the liquid surface, the growth will take place along the whole long side, thus the asgrown crystal has enough length in the xðaÞ direction, despite its very slow growth rate in this direction. Finally, we obtain large crystals of KTP with big Z-cut crosssection, as shown in Fig. 1. Using ITSSG, we can make the length in the xðaÞ direction of KTP crystals exceed 60 mm, furthermore, after enough growth cycles, it can even exceed 70, 80 mm, and so on.
674
X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
above-mentioned aspect, the reduction of temperature is usually not a constant. 3. E-O applications of KTP
Fig. 1. As-grown KTP crystals with big Z-cut crosssection by the ITSSG method.
Although there are many reports on the E-O applications of KTP crystals [8–10], the samples used were mostly grown by the hydrothermal technique. We have carried out some experiments for the E-O applications of the KTP; all the KTP samples used in these experiments were grown by the flux method. 3.1. KTP E-O waveguide
To grow high-quality KTP crystals without any liquid inclusion, the set procedure of lowering temperature is very important besides other growth parameters. We set the procedure of lowering temperature according to two factors, the first is the area of the total growth surfaces which can ‘‘accept’’ the growth unit. Obviously, great area means a great ability to ‘‘accept’’ the growth unit, and it means ability of growth, so we can lower the temperature relatively fast; the second factor is the effect of stirring. The procedure of lowering the temperature is mainly set according to the first factor, but is adjusted in the middle of the growth period by the second factor. We consider the different stages during the period of crystal growth, at first, the stirring of the solution is not enough because the crystal is too small, when compared with the volume of the solution; therefore, only the solute in the supersaturated solution near the crystal can reach the growth surface. So the growth rate is relatively low. Next, as the crystal becomes larger, the stirring effect of solution by the crystal becomes larger. The stirred region may extend to much of the solution, then the solute far from the crystal approaches the growing surface. In this stage, the growth rate becomes very high, at this time, we usually reduce the lowing rate of temperature, even maintain the temperature as a constant. Finally, when the solute for the excess supersaturation has been spent, the growth rate becomes stable and corresponds to the cooling rate of the temperature. Considering the
Optical waveguides have been fabricated on the flux KTP substrate with the size 20 10 3 mm3 by using an ion-exchange process that is similar to that used in forming waveguides in the glass substrate, the waveguides formed in this way have an exchange-ion concentration depth profile and refractive-index profile, that is close to a complementary error-function distribution, device thermal stability is much better. 3.2. KTP E-O modulator KTP is a biaxial crystal with an orthorhombic structure (point group mm2). The crystallographic directions a, b, c correspond to the optic axes x, y, z, with c being the polar axis. When used in amplitude modulation, as per calculation, it is required that the KTP crystal be cut normal to the principal crystal axes, the direction of lightwave propagation coincides with the y-axis, and the electric field coincides with the z-axis. From consideration of KTP’s mm2 point symmetry, light-amplitude modulation for a beam propagating along the y-axis requires the beam to be polarized 451 relative to the x-axis with the electric field along the z (polar axis)-direction. It is important to note that the KTP crystal has in fact an arbitrary static birefringence, and it has to be compensated for. For the sake of convenience, we use a couple of bulk KTP crystals with the same dimensions, one bulk turned 901 to the other, to compensate for the static birefringence, just as shown in Fig. 2.
X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
675
Fig. 2. A couple of bulk KTP crystals with the same dimensions, the one bulk turned 901 to the other, to compensate for the static birefringence.
3.2.1. Compared with LiNbO3 Q-switch was formed by a couple of KTP crystals with the size 4 16 4 mm3. The y-faces were optically polished and Ar-coated, and the ( electrodes were deposited on the z-faces with 500 A of sputtered gold. We use a high-voltage pulse generator with 1 KHz repetition frequency as a driver, under the condition of switching pulsewidth of 120–1200 ns and leading and trailing edges of 5 ns, to modulate the light beam of CW Ti:Al2O3 laser with 800 nm wavelength. The test results displayed regular rectangular optical pulse figuration without any acoustic ringing, as shown in Fig. 3. The half-wave voltage is about 580 V. In the same condition, except for replacing the two KTP crystals by a piece of LiNbO3 crystal with the same dimensions (4 16 4 mm3), we can see a strong acoustic ringing, as shown in Fig. 4. The half-wave voltage is about 1800 V. Considering that the total length of two KTP crystals is twice that of one LiNbO3 crystal, we can say the dynamic half-wave voltage of KTP is about 30–40% less than that of LiNbO3. The dynamic half-wave voltage is the important criterion for Q-switch applications. Moreover, KTP has almost no acoustic ringing, which is just the drawback of LiNbO3 crystal. 3.2.2. Compared with KD*P Bulk high-speed traveling wave E-O modulator was also fabricated using a couple of KTP crystals with the size 4 8 16 mm3, the half-wave voltage is just 760 V, response time of the device is low up to 297 ps. By contrast, E-O modulator fabricated by the KD*P crystal usually has a half-wave voltage of 7–8 kV and, in addition, a large
Fig. 3. The oscillograph of switching a CW laserbeam of KTP crystals, regular optical pulse figuration can be seen.
Fig. 4. Replaced KTP of the same device used in Fig. 3 by LiNbO3, some higher-order acoustic oscillations during the pulse can be observed.
distributing capacity of the device because KD*P’s dielectric is as large as 40, thus the device has a very slow response speed and cannot be modulated at the subnanosecond level.
4. Conclusions From our work, we have developed an improved top-seeded solution growth. Using this method, we obtained KTP crystals with the size
676
X. Wang et al. / Journal of Crystal Growth 237–239 (2002) 672–676
60 60 50 mm3 which can obtain big Z-cut crosssection from as-grown crystals, this will be advantageous to cutting for its E-O application. We have also carried out some experiments for E-O applications using flux KTP crystals, and the results showed, based on both low half-wave voltage and lack of piezoelectric-induced parasitics, that KTP has promising potential for various E-O modulation applications other than its major role as a doubling crystal. However, KTP crystals by the flux technique have a lower production cost, this makes us see the possibility of its large-scale application. Our work has shown low-cost flux KTP to be a strong candidate for the E-O applications.
Acknowledgements We acknowledge the valuable contributions of Mr. Li Shicheng, Sui Zhan et al., for device
preparation, E-O experiments and for their other support and encouragement.
References [1] J.D. Bierlein, C.B. Arweiler, Appl. Phys. Lett. 49 (1986) 917. [2] J.D. Bierlein, A. Ferretti, L.H. Brixner, W.Y. Hsu, Appl. Phys. Lett. 50 (1987) 1216. [3] J.D. Bierlein, H. Vanherzeele, J. Opt. Soc. Am. B6 (1989) 622. [4] R.A. Laudise, R.J. Cava, A.J. Caporaso, J. Crystal Growth 74 (1986) 275. [5] P.F. Bordui, J.C. Jacco, G.M. Loiacono, R.A. Stolzenberger, et al., J. Crystal Growth 84 (1987) 403. [6] R.J. Bolt, H. de Haas, M.T. Sebastian, H. Klapper, J. Crystal Growth 110 (1991) 587. [7] P.J. Halfpenny, L.O. Neill, J.N. Sherwood, G.S. Simpson, et al., J. Crystal Growth 113 (1991) 722. [8] X.D. Wang, P. Basseras, R.J. Dwayne Miller, H. Vankerzeele, Appl. Phys. Lett. 59 (1991) 519. [9] Takunori Taira, Takao Kobayashi, IEEE J. Quantum Electron. 30 (1994) 800. [10] C.A. Ebbers, S.P. Velsko, Appl. Phys. Lett. 67 (1995) 593.