Self-injection locking of a diode laser to a high-quality-factor microresonator is widely used for frequency stabilization and linewidth narrowing. We constructed several microresonator-based laser sources with measured instantaneous linewidths of 1 Hz and used them for investigation and implementation of the self-injection locking effect. We studied analytically and experimentally the dependence of the stabilization coefficient on tunable parameters such as locking phase and coupling rate. It was shown that precise control of the locking phase allows fine-tuning of the generated frequency from the stabilized laser diode. We also showed that it is possible for such laser sources to realize fast continuous and linear frequency modulation by injection current tuning inside the self-injection locking regime. We conceptually demonstrate coherent frequency-modulated continuous wave LIDAR over a distance of 10 km using such a microresonator-stabilized laser diode in the frequency-chirping regime and measure velocities as low as sub-micrometer per second in the unmodulated case. These results could be of interest to cutting-edge technology applications such as space debris monitoring and long-range object classification, high-resolution spectroscopy, and others.

Abstract:We report the design of an all-fiber continuous wave Short-Wave Infrared source capable to output up to 700 mW of power at 1940 nm. The source is tunable over wavelength intervals comprised between 1850 nm and 2070 nm depending on its configuration. The output can be single or multimode while the optical signal to noise ratio ranges from 25 and 40 dB. The architecture is based on the integrated association of a fiber optical parametric amplifier and a Thulium doped fiber amplifier.

We propose and experimentally demonstrate an all-optical Nyquist sinc-shaped pulse train source based on intensity modulation and four-wave mixing. The proposed scheme allows for the tunability of the bandwidth and the full flexibility of the repetition rate in the limit of the electronic bandwidth of the modulators used through the flexible synthesis of rectangular frequency combs. With the ever-growing demand for telecommunication bandwidth, highly efficient spectral techniques are currently thoroughly investigated in order to optimize the capacity of fiber optics networks. Two digital techniques are commonly used: orthogonal-frequency division multiplexing (OFDM), where a superchannel composed of sincshaped subcarriers is generated, and Nyquist-WDM where the data symbols are carried by Nyquist-shaped pulses in the time domain [1]. Recently, the concept of orthogonal time-division multiplexing (O-TDM) of optically generated Nyquist pulses was demonstrated [2]. In this scheme, the ultra-short Nyquist pulses are generated all-optically and time multiplexed with no intersymbol interference (ISI), taking advantage of the orthogonality of Nyquist pulses. Various techniques to generate optical Nyquist pulses have been demonstrated including spectral reshaping of mode-locked laser [2] or fiber optical parametric amplification using one degenerated pump [3] or two dissimilar frequency pumps in order to achieve uniform pulse generation over a wide bandwidth [4]. These techniques allow for the generation of Nyquist pulses of a few picoseconds duration down to sub-picosecond. However, reducing the complexity of these schemes to a viable solution is not straightforward. Moreover, the generated Nyquist pulses exhibit a non-rectangular spectrum, which leads to the necessity of guard band between WDM channels. To overcome these limitations, another technique based on phase-locked flat-comb generation was demonstrated to obtain sinc-shaped pulse trains [5]. The proofof-principle setup was based on intensity modulators driven by radio-frequency (RF) tones. This simple setup is cost-effective, but the generated bandwidth remains limited to three times the electronic bandwidth of the modulators. In order to overcome the bandwidth limitation, we show that a nonlinear stage based on Kerr effect in highly nonlinear fiber (HNLF) can be used to expand the bandwidth of the generated comb while maintaining the high flexibility and reconfigurability advantages of the original technique. The proposed principle for the Nyquist sinc-shaped pulse train generation is sketched in Fig. 1. Three stages of rectangular-shaped in-phase optical frequency comb generators (RI-OFCG's) are used to achieve a Nyquist-sinc pulse train from an initial optical continuous wave (CW) [ Fig. 1(a)]. The first and third stages are based on intensity modulation, while the second stage is based on four-wave mixing (FWM) [6,7] combined with a wavelength selective switch (WSS) [8].At the first RI-OFCG stage, the CW input is modulated via an intensity modulator (IM 1 ...

The nonlinear coefficient and group velocity dispersion of a thulium-doped fiber near 2μm are evaluated via four-wave mixing. Nonlinearity of thulium-doped fiber can be used for the design of doped-fiber lasers in this spectral region.

The stabilization and manipulation of laser frequency by means of an external cavity are nearly ubiquitously used in fundamental research and laser applications. While most of the laser light transmits through the cavity, in the presence of some back-scattered light from the cavity to the laser, the self-injection locking effect can take place, which locks the laser emission frequency to the cavity mode of similar frequency. The self-injection locking leads to dramatic reduction of laser linewidth and noise. Using this approach, a common semiconductor laser locked to an ultrahigh-Q microresonator can obtain sub-Hertz linewidth, on par with state-of-the-art fiber lasers. Therefore it paves the way to manufacture high-performance semiconductor lasers with reduced footprint and cost. Moreover, with high laser power, the optical nonlinearity of the microresonator drastically changes the laser dynamics, offering routes for simultaneous pulse and frequency comb generation in the same microresonator. Particularly, integrated photonics technology, enabling components fabricated via semiconductor CMOS process, has brought increasing and extending interest to laser manufacturing using this method. In this article, we present a comprehensive tutorial on analytical and numerical methods of laser self-injection locking, as well a review of most recent theoretical and experimental achievements.