Christoph Weber

Picosecond pulse amplification up to a peak power of 42 W by a quantum-dot tapered optical amplifier and a mode-locked laser emitting at 126 µm

We experimentally study the generation and amplification of stable picosecond-short optical pulses by a master oscillator power-amplifier configuration consisting of a monolithic quantum-dot-based gain-guided tapered laser and amplifier emitting at 1.26 µm without pulse compression, external cavity, gain- or Q-switched operation. We report a peak power of 42 W and a figure-of-merit for second-order nonlinear imaging of 38.5  W2 at a repetition rate of 16 GHz and an associated pulse width of 1.37 ps.

Monolithic passively mode-locked semiconductor quantum-well laser emitting at 1070 nm: Picosecond pulse generation and pulse train stability analysis

We study experimentally the pulsed emission of a passively mode-locked multi-section quantum-well semiconductor laser emitting picosecond short optical pulses at a fundamental repetition rate of 20 GHz and at a wavelength of 1070 nm. We identify different regions of picosecond short pulses dependent on the laser biasing conditions and relate them to the investigated mode-locking stability by means of timing jitter and amplitude jitter analysis. We obtain timing jitter values in a two-digit femtosecond range and operating regions without relative amplitude jitter at pulse widths in the order of a few picoseconds.

Impact of long external fiber cavities on the pulse train stabilization of a passively mode-locked quantum dot laser emitting at 1250 nm

Passively mode-locked (PML) semiconductor lasers are compact photonic sources delivering a train of picosecond short optical pulses for optical clock distribution, high bit-rate optical time division multiplexing and compact microwave/millimeter-wave signal generation. The pulse train can exhibit considerable timing jitter (TJ). We extend the recently studied impact of dual long-cavity optical feedback (DLC OFB) by investigating the impact of two long external fiber cavities on the timing and amplitude stability as well as the pulse repetition rate (RR). Modeling results by a simple time-domain model allow to reproduce the experiments with good agreement.

Multi-gigahertz picosecond pulse generation by passive mode-locking of monolithic two-section quantum well semiconductor lasers emitting at 1070 nm: Study of different laser lengths and gain-to-absorber section length ratios

Monolithic two-section quantum well semiconductor lasers are promising sources for the generation of short pulses in the single-digit picosecond range by passive mode-locking and at high pulse repetition frequencies exceeding 40 GHz. Laser emission at around 1070 nm makes them ideal candidates for potential light amplification in Ytterbium doped fiber amplifiers and application in data transmission experiments. In both, a precise knowledge of the pulse train stability, quantified by timing-jitter and amplitude jitter, is crucial. We experimentally investigate lasers with different cavity lengths and gain-to-absorber section length ratios. For a large variety of biasing parameters, the pulse generation performance and pulse train stability is quantified.

Timing jitter and multi-gigahertz pulse train repetition rate control of a long monolithic multi-section quantum dot semiconductor laser

Microwave/millimeter-wave signal generation and optical data communication applications demand compact, ultrafast and frequency agile mode-locked lasers. Monolithic semiconductor quantum dot lasers are attractive sources for such time-critical applications. Their repetition frequency is fixed by the laser cavity length and fine-tuning is limited. All-optical or opto-electrical laser stabilization schemes already allow for an improved frequency tuning, they however increase slightly the degree of complexity of the experiment. We present results on the timing jitter and repetition rate control of a monolithic mode-locked semiconductor laser by a specific absorber and gain section placement. We report on wide repetition rate frequency agility and substantial timing jitter reduction simply by gain current biasing.

Pulse train timing stability improvement and repetition frequency control of a monolithic mode-locked two-section quantum well semiconductor laser emitting at 1070 nm by all-optical self-feedback configurations

Compact monolithic passively mode-locked semiconductor lasers offer repetition frequencies in the Multi-GHz range and the generation of picosecond-short optical pulses. Their pulse train timing stability however, is considerable lower as compared to fiber-based pulsed lasers. All-optical self-feedback configurations have been studied that allow to substantially improve the timing stability. We present recent experimental results on the pulse train stabilization of a monolithic two-section quantum-well (QW) semiconductor laser emitting at 1070 nm by different fiber-based feedback configurations. Besides the timing jitter (TJ), we study the repetition frequency control and its dependence on the feedback-cavity parameters (e.g. feedback strength, coarse and fine delay lengths).

Ultralow pulse-to-pulse timing jitter for telecommunication applications by a monolithic passively mode-locked multi quantum-well semiconductor laser emitting at 1080 nm

Photonic data transmission in novel telecommunication applications demands picosecond-short optical pulses at a multi-GHz repetition-rate (RR) with low pulse-to-pulse timing jitter (TJ). While nowadays mostly wavelengths around 1.55 μm are used, ytterbium-doped fiber amplifiers allow for data transmission over long distances at wavelength of around 1050 nm. Exemplary photonic transmission in this wavelength region has been demonstrated by a mode-locked (ML) multi quantum-well (MQW) semiconductor laser subject to an external cavity delivering a pulse width (PW) of 22 ps at a RR of 10 GHz, a harmonic of the external cavity (EC) frequency, yielding an integrated TJ of 120 fs (100 Hz to 100 MHz) [1]. Initial investigations on a monolithic MQW semiconductor laser emitting at 1070 nm have recently been presented [2]. In this work, we present a monolithic passively ML InGaAs MQW ridge waveguide laser that generates a stable train of picosecond-short optical pulses at a wavelength of 1080 nm with a RR of 40 GHz and a very low TJ of 55 fs. The optical pulses are Gaussian shaped and their width can be as short as 4.6 ps. Beam profile analysis confirms a Gaussian beam shape with a beam aspect ratio of 0.71 allowing for an efficient single-mode fiber coupling. The laser is a 1 mm long multi-section structure with an absorber-to-gain-section length ratio of 0.1 (Fig. 1). The facets are as cleaved. Pulse properties are analysed in a wide range of laser gain injection current (GC) and absorber reverse bias voltage (RBV). The PW are obtained from Gaussian fits to the Autocorrelator (AC) time traces. The TJ can be calculated from the RR and the RR linewidth (Δf) by TJptp = (Δf / (2π RR3))0.5 [3]. Beam profile analysis is performed by near-field imaging analysis. By using a 60x microscope objective and a CCD camera, a homogeneous Gaussian shaped profile is confirmed, as depicted on the right in Fig. 1. An aspect ratio of 0.71 is obtained by Gaussian fits to the horizontal and the vertical axes, indicating an excellent beam profile for efficient single-mode fiber-coupling. The TJ for two selected absorber reverse biases voltages of 1.8 V and 2.0 V and for increasing GC are depicted in Fig. 2. The lowest TJ amounts to 55 fs at an RBV of 1.8 V and a GC of 410 mA. The corresponding RR line with a Lorentzian fit (−3-dB linewidth: 1.43 MHz) and the corresponding AC trace with a Gaussian fit yield a deconvoluted PW of 4.6 ps, as depicted as insets in Fig. 2. The color-coded TJ performance for a selection of driving parameters is depicted in Fig. 3. The region indicated by blue colour coding at high GC and low RBV depicts TJ values below 100 fs.

Stability criteria of a tapered InAs/InGaAs quantum dot laser based on pulse amplitude jitter and timing jitter investigations

Potential photonic imaging and time-critical applications based on passively mode-locked semiconductor lasers require a precise knowledge of instabilities of these ultra-short pulse sources. These instabilities mainly manifest in a decreased timing jitter and amplitude jitter of the generated optical pulse train. Their origins are a net gain window outside the optical pulse or an imbalance of gain and absorption. We quantify these instabilities by the analysis of the radio-frequency spectrum yielding the amplitude and timing jitter. Thus we can experimentally identify different mode-locking operation regimes.

Pulse train stability of multi-gigahertz passively mode-locked semiconductor lasers

Passively mode-locked semiconductor lasers have evolved as versatile photonic sources delivering ultra-short optical pulses with multi-gigahertz pulse repetition rates. In particular time-critical applications involving such compact and ultrafast photonic sources demand a precise knowledge of the pulse train timing and potential amplitude instabilities as well as pulse repetition control. The particular ultrafast gain and absorption dynamics in quantum dot based passively mode-locked lasers allows for ultra-short, stable pulse train generation [1], whereby the stability is limited by the timing noise stemming from the amplified spontaneous emission contribution [2]. Also, the laser can be amplitude-modulated by Q-switching instabilities, also known as Q-switched mode-locking, at frequencies from the MHz to the GHz range due to undamped relaxation oscillations [3]. To improve these timing- and amplitude instabilities, besides the proper laser layout design [4], several concepts have been developed experimentally and studied numerically including hybrid mode-locking [5], dual-mode optical injection [6], all-optical feedback schemes [7-11] or a combination of optical injection and optical feedback [13].

Experimental investigations on the generation and amplification of high power short pulses by a quantum dot laser and amplifier

In this paper, we study experimentally the generation of picosecond short optical pulses with an improved peak power of 42 W at a repetition rate of 16 GHz and an associated pulse width of 1.4 ps. Pulses from a tapered quantum dot laser emitting at 1250 nm are amplified using a tapered quantum dot optical amplifier without any pulse post-compression. We specifically investigate the amplification behavior of this master-oscillator power-amplifier configuration with a focus on the pulse peak power, pulse width, average power and amplified spontaneous emission towards improving the figure of merit for two photon excitation microscopy.