Ahmet E. Akosman

Dual comb generation from a mode-locked fiber laser with orthogonally polarized interlaced pulses

Ultra-high precision dual-comb spectroscopy traditionally requires two mode-locked, fully stabilized lasers with complex feedback electronics. We present a novel mode-locked operation regime in a thulium-holmium co-doped fiber laser, a frequency-halved state with orthogonally polarized interlaced pulses, for dual comb generation from a single source. In a linear fiber laser cavity, an ultrafast pulse train composed of co-generated, equal intensity and orthogonally polarized consecutive pulses at half of the fundamental repetition rate is demonstrated based on vector solitons. Upon optical interference of the orthogonally polarized pulse trains, two stable microwave RF beat combs are formed, effectively down-converting the optical properties into the microwave regime. These co-generated, dual polarization interlaced pulse trains, from one all-fiber laser configuration with common mode suppression, thus provide an attractive compact source for dual-comb spectroscopy, optical metrology and polarization entanglement measurements.

Low Noise, Mode-Locked 253 MHz Tm/Ho Fiber Laser With Core Pumping at 790 nm

We demonstrate a single-mode Tm/Ho co-doped mode-locked fiber laser with a repetition rate of 253 MHz that is directly core pumped at a wavelength of 790 nm. In a soliton mode-locked linear fiber laser cavity, femtosecond pulses with transform-limited pulse durations of 315 fs are generated. With single-mode core pumping, the high peak absorption of the gain medium is utilized to obtain an optical spectrum with suppressed ripples and high signal-to-background levels in the RF spectrum above 70 dB. Good noise performance with a rms relative intensity noise of 0.11% [10 Hz, 2 MHz] and a timing jitter of 20 fs [100 Hz, 2 MHz] is demonstrated. For a single pulsing mode-locking regime, a reproducible and stable peak wavelength tunability of the optical spectrum is achieved over 11 nm by pump power tuning.

Route towards extreme optical pulsation in linear cavity ultrafast fibre lasers

Pathways towards the generation of extreme optical pulsation in a chaotic transition regime in a linear fibre laser cavity configuration are presented. In a thulium mode-locked fibre laser, extreme events that can be controllably induced by manipulating the cavity birefringence for pulse energies exceeding the single soliton pulse operating regime are studied in detail for the first time. While a solitonic pulsation structure at the fundamental repetition rate is maintained, additional energy is shed in a chaotic manner, leading to broader spectral generation and shorter pulse durations whose behaviour deviates significantly from a classical statistical distribution. These pulses display markedly different characteristics from any previously reported extreme events in fibre lasers associated with multiple solitons and pulse bunching, thus presenting a novel observation of extreme pulsation. Detailed noise studies indicate that significant enhancement of relaxation oscillations, modulation instability and the interplay with reabsorption mechanisms contribute in this transient chaotic regime. The extreme pulsation generated in a compact fibre laser without any additional nonlinear attractors can provide an attractive platform to accelerate the exploration of the underlying physics of the chaos observed in mode-locked laser systems and can lead to novel fibre laser cavity designs.

Tm/Ho co-doped pulsed fiber laser with low spectral and temporal noise

A Tm/Ho co-doped mode-locked soliton fiber laser design is presented with stable and low noise single-pulsing operation at a repetition rate of 135.2 MHz and a transform limited pulse duration of 375 fs. The fiber laser is directly core pumped at a wavelength of 790 nm. In single-pulsing operation, the fiber laser is centered at a wavelength of 1983 nm and can be continuously tuned over an 8 nm bandwidth. The fiber laser consists of a linear cavity which allows scaling of the repetition rate further by reducing the cavity length and utilizing the high pump absorption at 790 nm and efficient absorption/emission dynamics without photodarkening. In addition, co-doping with Tm/Ho increases the efficiency of the lasing with enhanced cross-relaxation rates. Stable mode-locked operation with reduced ripples in the optical spectrum and high signal-to-background ratios in the RF spectrum is observed. A low relative intensity noise with an rms fluctuation level of 0.13 % (frequency interval of 10 Hz to 1 MHz) and a low phase noise with a timing jitter of 20 fs (frequency range of 100 Hz to 1 MHz) characterizes the mode-locked laser.