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Wavelength Meter Resolution vs Optical Spectral Resolution

When discussing the characteristics of the laser characterization tool, a really common confusion occurs between the terms “Optical Spectral Resolution” and “Wavelength Meter Resolution”. Indeed, both of these specifications contain the word “resolution” and are amongst the most common specifications of these characterization tools, but are referring to two widely different characteristics. The aim of this article is thus to well define both of the specifications and illustrate them by an example to avoid any mix up between the 2….


Efficient multi-mode fiber to single-mode fiber coupling: High speed VCSEL characterization

This article aims at illustrating the MMF to SMF coupling using a multimode scrambler, as introduced in a previous article, to couple a Vertical Cavity Surface Emitting Diode Laser (VCSEL) laser into a ZOOM Spectra high resolution Laser Spectrum Analyzer. Indeed, VCSEL laser are really compact semiconductors laser diodes with large Numerical Aperture emission beam perpendicular to their top surface, as illustrated figure 1. VCSEL are generally fabricated by batch of millions units on a wafer using standard semiconductor technologies….


Efficient multi-mode fiber to single-mode fiber coupling: comparison between the existing solutions

As described in a previous article, achieving an efficient light coupling from multimode fiber (MMF) to single mode fiber (SMF) is a difficult task, especially when trying to avoid any spectral losses while keeping an acceptable power conversion. The fiber to fiber coupling option, as well as the tapered fiber solution and the lenses system being discarded, other alternatives coupling systems have to be investigated. In the following article, the most common coupling setup, the integrating sphere as well as…


Efficient multi-mode to single-mode fiber coupling: introduction

The coupling of the optical signal from a multi-mode to a single-mode fiber is a critical issue in application fields that involve numerical aperture optical systems and high accuracy optical characterization tools, such as astronomy and laser testing. Indeed, such multi-mode to single-mode coupling is virtually impossible without loss of spectral information while keeping an acceptable power output. These articles will be aimed at screening the possible setups for such coupling, and finding the ones that offer the best trade-off…

What is a Laser Spectrum Analyzer?

A Laser Spectrum Analyzer (LSA) can be defined as a high resolution spectrometer aimed at the characterization of narrow linewidth light sources. In other words it measures the spectral density of a laser as a function of the wavelength. These instruments are typically used to check the spectral purity of laser sources, or to measure their Full Width Half Maximum. It exists two main methods to perform spectral analysis: Grating based Laser Spectrum Analyzers: Using one or several diffraction grating…

How to phase modulate a laser: the Pockels effect

As discussed in a previous article, the phase modulation of a laser is used in ICF (Inertial Confinement Fusion) in order to prevent any damage to the system. The goal of this article is to present how this phase modulation is usually carried out. The phase modulation is accomplished using the Pockels effect created in the so-called Pockels cells. These cells are electro-optic crystals through which the light can propagate and the phase delay is modulated by the electric voltage…

RES - Kit enseignement Transformée de Fourier et caractérisation Laser - IUT Grenoble

How to address laser spectrum analysis and signal processing in a practical way with undergraduate students?

In order to answer this question, we asked Dr. Guillermo Martin, professor at Grenoble Alpes University, which practical cases he set up to address these topics with his students. Hello Guillermo. Could you please introduce yourself and describe your professional background? I did a joint Ph.D between ENS-Cachan and the University of Madrid on the study of nonlinear optics in organic material for frequency conversion. In 2006 I joined the IPAG (Institut de Planétologie et d’Astrophysique de Grenoble) laboratory where…

Why phase modulating the lasers used in ICF

Within the past few decades, several major Inertial Confinement Fusion (ICF) facilities using high power lasers have been built around the world. The two largest ICF lasers currently in operation, the Laser Mégajoule (in Bordeaux, France), and the National Ignition Facility (in Livermore, CA, USA), both generate enough energy (1015 Watts/cm2) to initiate the fusion reaction of two hydrogen isotopes, or to replicate the conditions of a nuclear explosion. Figure 1 : Inertial confinement fusion process Courtesy of National Ignition…