Mikael Malmström

High-speed electrical switching in optical fibers [Invited]

In this paper, we give an overview of recent results on switching of light in fibers with internal electrodes. Polarization rotation, nanosecond gating, and wavelength switching in fiber Bragg gratings and in long period gratings are discussed. Applications are exemplified in Q-switching fiber lasers and in RF-signal filtering.

All-fiber cavity dumping

Cavity dumping of an all-fiber laser system is demonstrated. The active element is a pulse-picker with nanosecond rise time consisting of a microstructured fiber with electrically driven internal electrodes. The device is used for intracavity polarization rotation and dumping through a polarization splitter. The optical flux is removed from the cavity within one roundtrip and most of the amplified spontaneous emission, spiking and relaxation oscillation that follow during the gain recovery phase of the laser are blocked from the output signal.

Soliton generation from an actively mode-locked fiber laser incorporating an electro-optic fiber modulator

This work demonstrates an actively mode-locked fiber laser operating in soliton regime and employing an all-fiber electro-optic modulator. Nonlinear polarization rotation is utilized for femtosecond pulse generation. Stable operation of the all-fiber ring laser is readily achieved at a fundamental repetition rate of 2.6 MHz and produces 460 fs pulses with a spectral bandwidth of 5.3 nm.

Actively Q-switched all-fiber laser with an electrically controlled microstructured fiber

Actively Q-switching of an all-fiber laser system is demonstrated. The active element is a polarization switch with nanosecond risetime based on a microstructured fiber with electrically driven internal electrodes. Optical feedback between two 100% reflectors is inhibited until a nanosecond current pulse Q-switches the laser. After a short optical pulse develops several roundtrips later, the fiber switch is turned off, removing the short optical pulse from the cavity through a polarization splitter. Pulses of 50 W peak power and approximately 12 ns duration are obtained with 400 mW pump power at 100 Hz.

Pulse selection at 1 MHz with electrooptic fiber switch

Two 78-cm long electrooptic fibers with nonlinear coefficient χ((2)) ~0.26 pm/V are used in a Sagnac loop for pulse selection at up to 1 MHz repetition rate. Laser pulses of 1.5 µm wavelength arriving at every 140 ns are selected with an extinction ratio as high as -30 dB. The arrangement is entirely based on silica fiber.

Accurate modeling of high-repetition rate ultrashort pulse amplification in optical fibers.

A numerical model for amplification of ultrashort pulses with high repetition rates in fiber amplifiers is presented. The pulse propagation is modeled by jointly solving the steady-state rate equations and the generalized nonlinear Schrödinger equation, which allows accurate treatment of nonlinear and dispersive effects whilst considering arbitrary spatial and spectral gain dependencies. Comparison of data acquired by using the developed model and experimental results prove to be in good agreement.

Dynamics of long-period gratings tuned with internal fiber electrodes

The physics of electrically switched long-period grating in a twin-hole fiber with internal electrodes is studied. Dynamic measurements for the two polarizations show how the grating spectra shift in time due to the mechanical stress and heat transfer in the core and the cladding.

All-Fiber Q-Switched and Cavity Dumped Laser Using an Electrically Addressed Microstructured Fiber

We report on a pulsed fiber laser with two regimes of operation, one where cavity-roundtrip pulse durations are produced (85 ns long, 40 Wpp) and one with high power pulses (2 ns long, 148 Wpp).

Numerical study and validation of ultra-short pulse amplification in fiber amplifiers at high repetition rates

We present a numerical method for studying fiber-based ultra-short pulse amplification at high repetition rates. Validation of the simulations, by comparison with experimental results, are also presented.

All-Fiber Nanosecond Gating for Time-Resolved Spectral Analysis

We demonstrate the addition of time gating to a standard optical spectrum analyzer (OSA) operating in the spectral region ~1.06μm . This is accomplished by opening for 7 ns the optical input to the OSA with an electrically driven poled fiber in a Sagnac loop. The sequential interrogation with nanosecond resolution of the reflection from three fiber Bragg gratings along a piece of fiber allows distinguishing the spectral peaks created with a minimum separation of 85 cm. The passive extinction ratio of this device is >40 dB and returns to >40 dB from >23 dB on a 35-ns time scale directly after time gating.