Mode locking | EPFL Graph Search

Mode locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10−12 s) or femtoseconds (10−15 s). A laser operated in this way is sometimes referred to as a femtosecond laser, for example, in modern refractive surgery. The basis of the technique is to induce a fixed phase relationship between the longitudinal modes of the laser's resonant cavity. Constructive interference between these modes can cause the laser light to be produced as a train of pulses. The laser is then said to be "phase-locked" or "mode-locked". Laser cavity modes Although laser light is perhaps the purest form of light, it is not of a single, pure frequency or wavelength. All lasers produce light over some natural bandwidth or range of frequencies. A laser's bandwidth of operation is determined primarily by the gain medium from which the laser is constructed, and the range of frequencies over which a lase

High Performance InP-Based Quantum Dash Semiconductor Mode-Locked Lasers for Optical Communications

Anthony Martinez

Several applications are pushing the development of high performance mode-locked lasers: generation of short pulses for extremely high bit rate transmission at 100 Gb/s and beyond, all-optical clock recovery at 40 Gb/s and beyond, generation of millimeter wave signals through mode-beating on a high speed photodiode, optical sampling for analog-to-digital conversion, and generation of wavelength-division-multiplexing channels. This paper will report on new advances in InP-based quantum dash mode-locked lasers, which largely surpass the performance of their bulk or quantum well counterparts in terms of the mode-beating spectral purity and the bandwidth of optical spectrum. In particular, we will describe the quantum dash nanostructures used for the mode-locked lasers and the dependence of the mode-locking properties on detailed quantum dash structures. We will demonstrate that these quantum dash lasers can be actively mode-locked, generating sub-picosecond or picosecond pulses at different repetition frequencies with extremely low timing jitter. They can also be used to achieve all-optical clock recovery, with timing jitter compliant with International Telecommunication Union (ITU) standards even for highly degraded input optical signal-to-noise ratio. Finally, we demonstrate that, owing to the very wide and flat optical spectrum and the low relative-intensity noise level of the mode-locked laser, error-free transmission over 50 km single mode fiber has been achieved for eight wavelength division multiplexing ITU channels at 10 Gb/s with a channel spacing of 100 GHz. (C) 2009 Alcatel-Lucent.

2009

Self-Injection Locking of a Gain-Switched Laser Diode

Andrey Voloshin

We experimentally observe a self-injection locking regime of the gain-switched laser to a high-Q optical microresonator. We reveal that the comb generated by the gain-switched laser experiences a dramatic reduction of comb-teeth linewidths in this regime. We demonstrate the Lorentzian linewidth of the comb teeth of sub-kHz scale as narrow as for a nonswitched self-injection locked laser. Such a setup allows generation of high-contrast electrically tunable optical frequency combs with tunable comb-line spacing in a wide range from 10 kHz up to 10 GHz. The characteristics of the generated combs are studied for various modulation parameters & mdash;modulation frequency and amplitude, and for parameters, defining the efficiency of the self-injection locking & mdash;locking phase, coupling efficiency, and pump frequency detuning.

AMER PHYSICAL SOC2021

Photosensitivity and bragg grating technology for upconversion all-fiber lasers

Marcel Zeller

Fiber lasers are compact lightsources with high intrinsic beam quality and high efficiency. The lasing spectrum ranges from the blue to the near infrared and is achievable using fibers with different dopants and glass compositions. All-fiber lasers are characterized by a high attainable stability and are also available in the pulsed regime. A widespread range of applications for all-fiber lasers exists in the domain of telecommunications as well as in the medical domain. The first part of this work is dedicated to the characterization of fluoride glasses regarding photosensitive effects. Fluoride glasses allow several lasing transitions, which are not available in silicate glasses. Photosensitive effects in fluoride glasses would pave the way to fabricate fiber Bragg gratings in fluoride fibers. Fiber Bragg gratings can act as laser mirrors and are a necessary tool on the way to all-fiber lasers with an output beam inside a fiber tail. In this work, doped and undoped fluoride glasses are exposed to different ultraviolet lasers and induced refractive index changes are investigated by changes of their absorption spectra. Index changes higher than 10-4 have been obtained. The second part is dedicated to demonstrate novel upconversion laser configurations in the visible spectral range using fiber Bragg grating technology in germanosilicate fibers and upconversion in fluoride fibers. Upconversion lasing in the green, orange and red spectral range were demonstrated. Tuning over 8 nm was shown for the orange laser. To minimize intracavity losses, mode field diameter adapter in germanosilicate fibers have been realized. The incorporation of an all-fiber accousto optic phase modulator inside the cavity allows pulsed operation of the upconversion laser. Mode locking is demonstrated at the red wavelength with pulse durations below 100 ps. In conclusion, the potential to fabricate Bragg gratings in Cerium doped and undoped fluoride glasses was demonstrated. Furthermore, green, orange and red lasing of an all-fiber configuration has been shown by a hybrid approach based on fiber Bragg grating technology in germanosilicate fibers and upconversion in fluoride fibers. An all-fiber mode locked upconversion laser in the red spectral range was demonstrated. We believe that such novel upconversion light sources represent a useful tool in different biomedical applications.

EPFL2004

Photosensitivity and bragg grating technology for upconversion all-fiber lasers

Marcel Zeller

EPFL2004