Search results for " feedback"

Fiber laser switched by a long period grating interferometer as an intra-cavity loss modulator

2010

Abstract In this paper we present an actively switched fiber laser with an all-fiber long-period grating-based interferometer used as an intra-cavity loss modulator. The modulator consists of two equal long-period gratings written sequentially in the same piece of a double-clad optical fiber. One of the gratings is fixed onto a piezoceramic cylinder producing fast modulation of the interferometer transmission spectrum. The laser demonstrates a stable regime of pulsed emission at repetition rates in the range of tens of kHz.

Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating.

2009

We report active Q-switching of an all-fiber laser using a Bragg grating based acousto-optic modulator. Q-switching is performed by modulating a fiber Bragg grating with an extensional acoustic wave. The acoustic wave modulates periodically the effective index profile of the FBG and changes its reflection features. This allows controlling the Q-factor of the cavity. Using 1 m of 300 ppm erbium-doped fiber and a maximum pump power of 180 mW, Q-switch pulses of 10 W of peak power and 82 ns wide were generated. The pulse repetition rate of the laser can be continuously varied from few Hz up to 62.5 kHz.

Fiber laser with combined feedback of core and cladding modes assisted by an intracavity long-period grating

2011

We present a fiber laser made in a single piece of conventional doped-core fiber that operates by combined feedback of the fundamental core mode LP((0,1)) and the high-order cladding mode LP((0,10)). The laser is an all-fiber structure that uses two fiber Bragg gratings and a long-period grating to select the modes circulating in the cavity; the laser emits at the coupling wavelength between the core mode LP((0,1)) and the counterpropagating cladding mode LP((0,10)) in the Bragg gratings. This work demonstrates the feasibility of high-order mode fiber lasers assisted by long-period gratings.

Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating

2009

We report an actively Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating. The laser employs a pair of Bragg gratings as reflective mirrors, one of which is bonded to a magnetostrictive element. Lengthening of the magnetostrictive element when a magnetic field is applied shifts the Bragg wavelength of the grating, allowing control of the Q-factor of the cavity and, thus, performing active Q-switching. The magnetostrictive modulator is small, compact and requires less than 300 mW electrical drive power. Using erbium-doped fiber and a maximum pump power of 120 mW, Q-switch pulses of more than 1 W peak power were obtained, with a pulse repetition rate that can be…

High-Resolution Nonlinear Raman-Spectroscopy in Gases

1990

0377-0486; The resolution in the Raman spectra of gases has been greatly improved by the development of the different methods of non-linear Raman scattering. When two laser beams, one of which has a tunable frequency, are focused in a sample, a stimulated Raman process occurs as soon as the frequency difference between the two lasers is equal to a Raman-active rovibrational or rotational transition frequency. The Raman resonance can be detected in different ways: by coherent anti-Stokes Raman scattering (CARS) or the corresponding Stokes process (CSRS), by a gain in one of the beams (stimulated Raman gain spectroscopy, SRGS) or a loss in the other (inverse Raman spectroscopy, IRS), or even …

Peer assessment based assignment to enhance interactions in online learning groups

2015

In this paper, we report on the findings from our PhD work on how peer assessment based assignment method can enhance interaction in online learning groups. The method is explored and tried out on the research methods course on the Bachelor of Commerce Programme which is run in distance learning mode at Makerere University. Based on the idea that learning groups can enhance effective learning in online learning environments, we used the affordance eLearning framework to design the peer assessment based assignment task and then qualitative methods collect and report on data. The results reveal that there was increased interaction through peer feedback. Students were motivated because of the …

Adaptive formative feedback to improve strategic search decisions in task-oriented reading

2014

This study analyses the effectiveness of adaptive formative feedback to boost strategic search decisions and performance when students are asked to answer a set of questions in a task-oriented reading situation. We compared automatic feedback that included information about the right answer with feedback that also included the connection between the students' strategic search decisions and their performance. Ninety-two high school students read two non-continuous texts. They received feedback during a training phase, and then they read and also received feedback with a similar text in a final phase. Text and questions were presented using a new computer-based technology that provided automa…

Motivating Low-Achievers—Relative Performance Feedback in Primary Schools

2021

Abstract Relative performance feedback (RPF) has often been shown to improve effort and performance in the workplace and educational settings. Yet, many studies also document substantial negative effects of RPF, in particular for low-achievers. We study a novel type of RPF designed to overcome these negative effects of RPF on low-achievers by scoring individual performance improvements. With a sample of 400 children, we conduct a class-wise randomized-controlled trial using an e-learning software in regular teaching lessons in primary schools. We demonstrate that this type of RPF significantly increases motivation, effort, and performance in math for low-achieving children, without hurting …

Individual Rank and Response: Survey-Based Evidence on the Effects of Rank-Based Performance Feedback

2021

A case study on gamified interventions for team cohesion in factory work

2018

In this article, we aim to provide insights into the design and implementation of game elements for teamwork on the work floor and to study their effect. Inventing games to break monotonous jobs is a long-standing practice, yet conscious implementation of motivational elements of games at work is a recent phenomenon. Generally, gamification is used to enhance individual performance; it may be effective in enhancing teamwork as well. We developed game elements aimed at team cohesion and examined the effect of two gamified interventions (team performance feedback and personal profiles) on team cohesion in a factory. Results suggest that the interventions mainly raised attention toward the asp…