IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 18, NO. 5, MARCH 1, 2006 721 Waveform-Controllable Optical Pulse Generation Using an Optical Pulse Synthesizer D. Miyamoto, Student Member, IEEE, K. Mandai, Student Member, IEEE, T. Kurokawa, Member, IEEE, S. Takeda, T. Shioda, and H. Tsuda, Member, IEEE Abstract—We have proposed an optical pulse synthesizer comprising of optical modulators and an arrayed waveguide grating. This system can generate arbitrary waveform pulses in combination with a broad-band optical frequency comb. We achieved the generation of the Gaussian pulses with a width of 4.7 ps, double-Gaussian pulses, and rectangular-shaped pulses by arbitrary waveform pulse synthesis, at the high repetition rate of 10 GHz. Index Terms—Arrayed waveguide grating (AWG), electrooptic modulation, frequency comb, optical pulse generation, optical pulses., optical pulse shaping, pulse shaping methods. I. INTRODUCTION H IGH repetition rate and stable optical short pulse sources that enable arbitrary control of the output waveform are required in the research field of optical communication systems. For example, mode-locked lasers are generally used for gener- ating the optical short pulses. However, their output waveforms cannot be controlled. We proposed a novel optical pulse synthesis system based on intensity and phase spectrum control of the optical frequency comb by using an arrayed waveguide grating (AWG) integrated with optical phase modulators and an intensity modulator [1]–[10]. The optical frequency comb generator consists of a single-wavelength continuous light source, optical phase mod- ulators, and an intensity modulator. The broad-band frequency comb was generated by modulating single-wavelength light using phase modulators with a large driving voltage [10], [11]. The repetition rate of the output pulse was very stable, because it was determined by the electrical synthesizer. The spectrum of the frequency comb was controlled by the AWG module. This enables the fabrication of intensity/phase modulator arrays on the same silicon substrate which can be used to control the spectrum of broad-band light. II. CONFIGURATION OF THE OPTICAL PULSE SYNTHESIZER The configuration of the optical pulse synthesizer is shown in Fig. 1. It consists of a frequency comb generator and a spectrum controller with an AWG. Manuscript received August 31, 2005; revised November 19, 2005. This work was supported by the Ministry of Public Management, Home Affairs, Posts and Telecommunications. D. Miyamoto, K. Mandai, and H. Tsuda are with Keio University, Yokohama 223-8522, Japan (e-mail: miyamoto@tsud.elec.keio.ac.jp). T. Kurokawa, S. Takeda, and T. Shioda are with Tokyo University of Agri- culture and Technology, Tokyo 184-8588, Japan. Digital Object Identifier 10.1109/LPT.2006.870080 Fig. 1. Schematic of the optical synthesizer, consisting of a frequency comb generator and a spectrum controller. A. Frequency Comb Generation The broad-band frequency comb enables the pulse synthe- sizer to generate shorter pulses and intricate waveform pulses. The broad-band spectrum can be generated by optical phase modulation with a large driving voltage and the spectrum can be flattened by intensity modulation [9], [10]. Fig. 2 shows two types of the frequency comb generation system. The light source is a tunable-wavelength laser. In Fig. 2(b), two LiNbO optical phase modulators were connected in series next to the optical source. One of these modulators was driven by the modulation voltage at the frequency of , and another is at the frequency of 2 . In Fig. 2(b), a single-arm-drive Mach–Zehnder inten- sity modulator was connected next to the phase modulators. In both types of the system, 10-GHz sinusoidal driving voltages were applied to the modulators through low-pass filters. Phase shifters were inserted between the pulse generator and the mod- ulators to adjust the relative phase differences between each driving signal. Fig. 3 shows the experimental frequency comb spectra using this optical frequency comb generation system (b). As shown in Fig. 3, the generated frequency comb had 21 modes within 3-dB bandwidth at 200 GHz. B. Spectrum Controller In order to synthesize arbitrary waveform optical pulses, the intensity and the phase of each mode of the frequency comb 1041-1135/$20.00 © 2006 IEEE