In this work, we compare ultrashort pulse generation in a monolithic two-section diode laser chip based on passive- and self- mode-locking (PML and SML) regimes at 1550 nm. In PML, we apply a forward current into the gain segment and a reverse voltage into the absorber segment. For SML operation, both segments are operated by applying a forward current. Strongly chirped pulses with an autocorrelation-width of roughly 7-8 picoseconds are obtained for both cases. We analyze the potential for fiber-based compression of the pulse widths down to the sub-picosecond range.
In this work, self-mode-locking of 100 GHz mode-locked pulses from a single-section InP quantum-dash-based laser chip whilst employed in external cavity geometry at 1550nm is investigated. The chip is operated at a forward current marginally above its monolithic operation's lasing threshold. Ultrashort pulses with 1 ps pulse- width were obtained by compensating the chirp by a single mode fiber (SMF).
In this work, a comparison of self-mode-locking of a 100 GHz repetition-rate monolithic diode as a stand-alone laser source and whilst employed in an external cavity arrangement at 1550 nm is reported. We operated our chip at a forward current slightly above the monolithic chip's lasing threshold and compensated the chirp by a single mode fiber. Ultrashort pulses with 1 ps pulse-width were generated. Changes in the dispersion compensation parameters due to the changed cavity dispersion were analyzed.
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.
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