We present a ring semiconductor amplifier system which is seeded by ultrashort pulses for additive amplification. An external cavity diode laser configuration is built to generate the ultrashort pulses based on a hybrid modelocking scheme. A monolithic multi-segment diode laser is utilized as a light source in the operating oscillator. It has the advantage that the gain and absorber are integrated on one chip. The oscillator operates at a fundamental repetition-rate of 206MHz and can be driven on various harmonics of this frequency. The generated pulses are injected into a tapered amplifier (TA) which consists of a ridge waveguide section (RWS) for coupling and a tapered section (TS) for amplification. The amplified pulses are coupled back after amplification towards the TAs RWS forming a ring resonator setup. By matching the cavity lengths of the oscillator and ring resonator, we can obtain additively amplified pulses. The emission spectrum of the chosen TA is centered around 850nm which is in the wavelength range of the oscillator. The spectrum of the additively amplified pulses is observed for different pumping parameters of the TA using an optical spectrum analyzer. Additionally, we characterized the system for the best seeding parameters by monitoring the output signal with an autocorrelator. We figured out that the best performance is achieved when the amplifier is seeded by pulses at the second harmonic of 412 MHz. When blocking the seeding pulses the amplifier operates in continuous wave (CW) regime. By comparing the obtained spectra for CW and additively amplified pulses, we conclude that the system operates with a CW background also in pulsed operation. However, from the comparison of the spectra, we estimate that the amplified pulsed power is about 120mW for a seed power of 1:1mW. Thus, the ring amplifier provides a significantly higher amplification than a single pass amplifier. In future work the CW background has to be suppressed, e.g. by synchronous modulation of the current into the amplifiers ridge waveguide section.
Semiconductor lasers are promising sources for generating ultrashort pulses. They are directly electrically pumped, allow for a compact design, and therefore they are cost-effective alternatives to established solid-state systems. Additionally, their emission wavelength depends on the bandgap which can be tuned by changing the semiconductor materials. Theoretically, the obtained pulse width can be few tens of femtoseconds. However, the generated pulses are typically in the range of several hundred femtoseconds only. Recently, it was shown that by implementing a spatial light modulator (SLM) for phase and amplitude control inside the resonator the optical bandwidth can be optimized. Consequently, by using an external pulse compressor shorter pulses can be obtained. We present a Fourier-Transform-External-Cavity setup which utilizes an ultrafast edge-emitting diode laser. The used InGaAsP diode is 1 mm long and emits at a center wavelength of 850 nm. We investigate the best conditions for passive, active and hybrid mode-locking operation using the method of self-adaptive pulse shaping. For passive mode-locking, the bandwidth is increased from 2.34 nm to 7.2 nm and ultrashort pulses with a pulse width of 216 fs are achieved after external pulse compression. For active and hybrid mode-locking, we also increased the bandwidth. It is increased from 0.26 nm to 5.06 nm for active mode-locking and from 3.21 nm to 8.7 nm for hybrid mode-locking. As the pulse width is strongly correlated with the bandwidth of the laser, we expect further reduction in the pulse duration by increasing the bandwidth.
Mode-locked semiconductor lasers are a promising source for applications such as ultrafast optical sampling. For such
an application, the reduction of timing jitter of the pulse source in a cost-effective manner is a key challenge. While
monolithic devices have been the source of much recent interest, external cavity lasers have been less well studied. In
this work, the noise of an external cavity laser under passively mode-locked operation is evaluated. A ridge-waveguide
super-large optical cavity material system is used.
Ultrashort pulse generation with semiconductor lasers poses a promising alternative to currently available femtosecond laser sources like solid state and fiber lasers. Semiconductor devices can be produced inexpensively, are energy efficient and their wavelength can be designed by band gap engineering. Furthermore they feature a tunable repetition rate. Yet pulse duration and peak power of those devices limit their potential for applications so far. However, recent research demonstrated a reduction of the pulse width from 534 fs (full width half maximum) to 216 fs by shaping the spectrally resolved spectral phase and amplitude inside the cavity. The utilized system consisted of a mode-locked edge emitting semiconductor laser diode, a spatial light modulator inside the external cavity to carry out the pulse shaping and an evolutionary algorithm to optimize the phase and amplitude. Here we present the results of separate phase and amplitude shaping as well as their interaction if optimized together at the same time. Furthermore we demonstrate the flexibility of the phase and amplitude shaping with respect to each other. Thus we expect of our system to enable adaptation to a resonator external dispersion.
We present intra-cavity pulse shaping of external cavity mode-locked semiconductor lasers. In our approach, a pulse shaper utilizing a dual LC-panel spatial light modulator is used in the cavity of a mode-locked multi-quantum-well semiconductor laser to introduce spectrally resolved phase manipulation and losses to the pulse propagating in the cavity. Utilizing this, we generate pulses with broader spectra than obtained in conventional external cavity geometries without pulse shaping. The pulses can be compressed near to the transform limit using a grating compressor.
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