Guillaume Brochu

Modeling and experimental demonstration of ultracompact multiwavelength distributed Fabry-Pe/spl acute/rot fiber lasers

This work presents a complete model for the design and optimization of multiwavelength distributed Fabry-Pe/spl acute/rot (DFP) fiber lasers that are made by superimposing two chirped fiber Bragg gratings in a photosensitive codoped erbium-ytterbium (Er-Yb) fiber. The model is based on a matrix formulation of coupled-mode equations taking into account the chirped grating superstructure and including a spectrally resolved gain medium. The performed analysis reveals that the signal power of each channel is strongly localized near a minimum of the superstructured-grating envelope. As a consequence, the overlap between the power distributions in neighboring cavities is small, thus reducing the effect of cross-gain saturation and allowing a high number of channels in a short piece of fiber. The simulations also show how the saturation of the cross-relaxation mechanism between ytterbium and erbium leads to flat output spectra without the need for an additional equalization scheme such as a complex grating apodization profile. Furthermore, to validate the theoretical model, we present the experimental realization and characterization of a multiwavelength laser emitting in a single-mode and single-polarization over 16 wavelengths spaced by 50 GHz and with a total output power of 52 mW.

SRS modeling in high power CW fiber lasers for component optimization

A CW kilowatt fiber laser numerical model has been developed taking into account intracavity stimulated Raman scattering (SRS). It uses the split-step Fourier method which is applied iteratively over several cavity round trips. The gain distribution is re-evaluated after each iteration with a standard CW model using an effective FBG reflectivity that quantifies the non-linear spectral leakage. This model explains why spectrally narrow output couplers produce more SRS than wider FBGs, as recently reported by other authors, and constitute a powerful tool to design optimized and innovative fiber components to push back the onset of SRS for a given fiber core diameter.

High-End FBG Design and Manufacturing for Industrial Lasers, Sensing and Telecommunications

This paper reviews how efficient design and manufacturing techniques for fiber Bragg grating-based components enables superior performances in optical communications, industrial lasers and sensing applications.

Dynamics of Hydrogen Diffusion as a Key Component of the Photosensitivity Response of Hydrogen-Loaded Optical Fibers

We present a new model predicting the photosensitivity response of hydrogen/deuterium-loaded optical fibers used for the fabrication of fiber Bragg gratings (FBGs). This model considers space- and time-dependent hydrogen concentration as a key phenomenon to explain the growth rates of strong index changes ( > 10-3). The model outputs are compared to several photosensitivity experiments made with three different fibers and different hydrogen-loading concentrations. The experimental results presented in this paper clearly show that the time interval between each step of the grating inscription has an impact on the overall photosensitivity response. Moreover, the proposed model confirms that the variations observed in the measured photosensitivity come from changes in hydrogen concentration resulting from its consumption by the photosensitivity reaction and its diffusion into the glass. This model will find application in the precise fabrication of strong FBGs by helping to predict the optimum writing conditions.

Fabrication of erbium-ytterbium distributed multi-wavelength fiber lasers by writing the superstructured fiber Bragg grating resonator in a single writing laser scan

We present an alternative method to fabricate multi-wavelength distributed-feedback fiber lasers made of superstructured chirped fiber Bragg gratings in a single writing laser scan with a custom period-profiled phase mask and a tailored amplitude apodization profile produced by phase mask dithering. This method simplifies the fabrication process and increases the yield of samples having the right number of laser lines and a small frequency error with respect to a reference grid.

Modeling of the Nonlinear Photosensitivity Response of Hydrogen-Loaded Germanium-Doped Optical Fiber in the Presence of Hydrogen Diffusion and Depletion

We present a novel model demonstrating the critical role of hydrogen diffusion and depletion in the nonlinear photosensitivity response of hydrogen loaded optical fibers during grating inscription. It provides answers to several experimental observations.

Measurement of intensity noise correlation between lines of spatially distributed multi-wavelength fiber lasers

Photoinscription of superstructured Bragg gratings in Er-Yb codoped fiber is a promising and cost-effective approach to produce high-quality multi-wavelength fiber lasers for various applications like radio-over-fiber systems, fiber-optic sensors or low-cost WDM testing source. However, a good understanding of the noise properties of the laser source is required before these applications can be addressed. Previous modeling has shown that these devices are similar to compact cascades of single wavelength DFB fiber lasers in which the modes at each wavelength are almost nonoverlapping along the fiber. In this paper, we further examine the independence of each channel by performing relative intensity noise (RIN) measurements on a multi-wavelength fiber laser, a dual-polarization fiber laser and a dualwavelength fiber laser. In each case, we estimate the correlation between the laser lines. From RIN measurements performed on each channel of a multi-wavelength laser, as well as on the full spectrum, we compute an average degree of correlation between the RIN of neighboring lines and observed no correlation in most of the cases. Moreover, each channel displays a single relaxation frequency which is different from those of the other channels. On the other hand, we observed strong partition noise, with negative correlation, between polarization modes of a single wavelength fiber laser. Finally, we measured the RIN of the two modes of a dual-wavelength fiber laser with modes having a greater overlap than the multi-wavelength laser. The results show that the lines share two common relaxation frequencies, an indication of a dynamic link between them.

Numerical investigation of the Raman instability in high-power CW ytterbium-doped fiber lasers

A numerical model of a high power CW ytterbium-doped fiber laser has been developed using the split-step Fourier method. Stimulated Raman scattering (SRS) is included in the model via the well-known Raman transfer function of silica fibers. The parameters of the gain fiber and of the fiber Bragg gratings are varied in order to minimize the impact of SRS on the spectral content of laser emission.

100 nm Wide Fiber Bragg Grating Dispersion Compensator Around Zero Dispersion Wavelength

Nonlinearly chirped fiber Bragg gratings compensate 600 ps of chromatic dispersion from 4 km of SMF-28 fiber around the zero dispersion wavelength with less than 10 ps of residual delay over a 100 nm bandwidth.

Multiwavelength ultracompact narrow-line all-fiber laser

An ultra-compact single-mode six-wavelength DBR fiber laser, with potential as a source for multi-channel fiber sensors, is demonstrated. Pumped with a single 150 mW 980-nm diode laser, the average power is 5 dBm per line.