CThN5 2005 Conference on Lasers & Electro-Optics (CLEO) Low jitter 1.55 pum dual semiconductor laser system with electrical phase shifter for quick ultrafast measurements C. Meuer, H. Quast, V. Eisner and D. Bimberg Institutfuier Festkoerperphysik, Technische Universitaet Berlin, PNS-2, Hardenbergstr. 36, 10623 Berlin, Germany chmeuer@sol.physik.tu-berlin.de Abstract: We present a dual semiconductor laser system at telecom wavelengths generating pulses below 300fs. The low-jitter temporal delay of up to 2ns is achieved electrically by a phase shifter enabling pump-probe measurements within short time. ©2005 Optical Society of America OCIS codes: (320.7100) Ultrafast measurements; (140.5960) Semiconductor lasers 1. Introduction Ultrafast pump-probe measurements such as electro-optical sampling (EOS) or terahertz time-domain spectroscopy (THz-TDS) require stable ultrashort pulse laser systems with temporal delay capabilities. Operation at telecom wavelengths allows not only the characterization of telecom devices by a backside probing scheme, but also the use of low-cost standard components which are especially interesting for a THz-TDS System. Here we present a stable all-fiber dual semiconductor laser system operating at a wavelength around 1.55 gm that generates high quality pulses below 300 fs FWHM at a repetition rate of 400 MHz. Both lasers are locked to the same high quality oscillator assuring superb jitter performance. The low-jitter temporal delay between the two lasers is achieved electrically by a phase shifter enabling higher mechanical stability, a much longer scan window (-2 ns) of about half the repetition rate and very fast temporal delay compared to a delay stage. The non-linear compression scheme to generate the ultrashort pulses is based on comb-like dispersion profiled fiber (CDPF) which design is optimized for each laser [1]. Such fast-scanning systems are of largest importance for the characterisation of e.g. photodetectors above 150 GHz via EOS [2]. First tests for its use in THz-TDS have also been performed. Here we concentrate on the performance and stability of the laser system itself to demonstrate applicability for measurements above 500 GHz. Optical cross-correlation measurements demonstrate the system bandwidth. Long-term temperature stability investigations ensure a turn-key system. The phase-shifter as the key for the system advantages is identified. In the following chapters the investigations regarding stability of such a system and its low-jitter perfornance is described in detail to demonstrate the feasibility of the use of an electrical phase shifter for temporal delay. 2. Theory and experimental results The pulse generation system is based on two self seeded and gain switched FP-laser diodes. Each is driven by electrical pulses of its own comb-generator. Both comb-generators are locked to the same crystal oscillator while in one path the electrical phase-shifter is placed. The optical pulses generated by this system are at first chirp compressed and then after amplification compressed to below 300 fs using an optimized soliton compression scheme based on CDPF. The pulse generation setup is shown schematically in fig 1 and the pulse compression using nonlinear effects is presented in fig. 2. Especially for EOS measurements a relatively weak pump pulse but an intense probe pulse are desired. This makes sure that the device under test is not damaged during the measurement and nevertheless the achievable sensitivity is satisfying. The system is completely fiber based for easier handling and consists only of commercially available components. 1781