ThP_122
Wavelength Dependence of Ridge-Waveguide Optical Phase Modulators Young Tae Byun, Young Min Jhon, and Sun Ho Kim Photonics Research Center, Korea Institute of Science and Technology (KIST), 39-1 Hawolgok, Seongbuk, Seoul 136-791, Korea Author email address:
[email protected]
Abstract The single mode GaAs/AlGaAs P-p-n-N ridge waveguide phase modulators have been fabricated and the phase shifts have been measured by using a Mach-Zehnder interferometer. The wavelength dependence of the phase modulators is reported between 1.06 µm and 1.55 µm.
1. Introduction
III-V semiconductor optical waveguide devices have been mainly investigated for applications in photonic integrated circuits. Recently, there has been an increasing interest in the development of the optical waveguide phase modulators and switches in GaAs- and InP- based structures [1-5]. Up to now many workers have concentrated on measuring the high phase modulation efficiency at λ=1.06∼1.15 µm using P-n-N [1,2], P-p-n-N [1], and P-i-N [2] doping structures. In addition, P-p-i-n-N [3] and P-P-p-i-n-N-N [4] structures have been studied to obtain the highest phase modulation efficiency at the 1.30 µm wavelength. For practical applications, the operational wavelengths of the phase modulators have to be studied in the wavelength range of 1.30∼1.55 µm. However, it has not been reported for a single-mode P-p-n-N GaAs/AlGaAs phase modulator at λ=1.06 ∼ 1.55 µm yet. In this paper, the wavelength dependence of the phase modulation efficiency is reported in a single-mode P-p-nN GaAs/AlGaAs phase modulator over the range of wavelengths for optical communication.
2. Experimental
Our P-p-n-N GaAs/AlGaAs ridge waveguide phase modulator is realized by inserting p- and n-GaAs layers between P- and N-AlGaAs cladding layers. An epitaxial structure of the P-p-n-N phase modulator is shown in Fig. 1. The epilayers were grown by a MOCVD technique on a (100) oriented Si doped GaAs substrate. Waveguides parallel to the [01 1 ] direction were made by conventional photolithography and wet chemical etching method described elsewhere [4]. The average waveguide widths are about 1.8 µm and the etch depth is about 1.99 µm. Phase modulators with a length of 2 mm were prepared by cleaving the sample. Phase shift measurements were performed using a Mach-Zehnder (MZ) interference technique [5]. Fringes of the MZ interferometer were scanned by applying a reverse bias voltage varying from 0 V to -5 V to change the optical phase [5]. The switching voltage (Vπ) is obtained to be as low as 1.6 V and 2.2 V for 1.31 µm and 1.55 µm wavelengths, respectively. The phase modulation efficiencies are estimated to be as high as 56.3
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and 40.9 ˚/V⋅mm for each wavelength. These efficiencies, to the best of our knowledge, are larger than the highest experimental value reported at the same wavelengths for reverse-biased GaAs/AlGaAs Phase modulators. Figure 2 shows the wavelength dependence of the phase modulation efficiency for TE mode as a function of wavelength. The modulation efficiency at 1.06 µm are obtained from the experimental data reported in reference 1. The efficiency is high at shorter wavelengths but decreases rapidly for longer wavelengths. The corresponding efficiencies are 96 ˚/V⋅mm at 1.06 µm, 56.3 ˚/V⋅mm at 1.31 µm, and 40.9 ˚/V⋅mm at 1.55 µm for TE modes.
Fig. 1 Epilayer structure and refractive index profile of
Fig.2 Wavelength dependence of the phase
P-p-n-N GaAs/AlGaAs waveguide phase modulators.
modulation efficiency for the TE polrarization.
3. Conclusions
The highly efficient P-p-n-N GaAs/AlGaAs ridge waveguide phase modulators have been fabricated and characterized to obtain the wavelength dependence. The phase modulation efficiencies were achieved to be as high as 56.3 and 40.9 ˚/V⋅mm at 1.31 µm and 1.55 µm for the TE polarization. Finally the wavelength dependence has been demonstrated at the wavelengths ranging from 1.06 µm to 1.55 µm.
4. References [1] G. Mendoza-Alvarez, L. A. Coldren, A.. Alping, R. H. Yan, T. Hausken, K. Lee, and K. Pedrotti, “Analysis of Depletion Edge Translation Lightwave Modulators,” J. Lightwave Technol., Vol. 6, pp.793-808 (1988). [2] J. Faist and F. –K. Reinhart, “Phase modulation in GaAs/AlGaAs double heterostructures. II. Experiment,” J. Appl. Phys., Vol. 67, pp. 7006-7012 (1990). [3] S. S. Lee, R. V. Ramaswamy, and S. Sundaram, “Analysis and design of high-speed high-efficiency GaAs-AlGaAs double heterostructure waveguide phase modulator,” IEEE J. Quantum Electron., Vol. QE-27, pp. 726-736 (1991). [4] Young Tae Byun, Kyung Hyun Park, Sun Ho Kim, Sang Sam Choi, Jong Chang Yi, and Tong Kun Lim, "Efficient single-mode GaAs/AlGaAs W waveguide phase modulator with a low propagation loss," Appl. Opt., Vol. 37, pp. 496- 501 (1998). [5] Young Tae Byun, Sung Jin Kim, Sun Ho Kim and Jong chang Yi, “Linear Electrooptic Coefficient of a GaAs/Al0.4Ga0.6As phase modulator,” J. Kor. Phys. Soc., Vol. 45, No. 5, pp. 1162-1164 (2004).
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