Bryan Burgoyne

Coherent anti-Stokes Raman scattering hyperspectral tissue imaging with a wavelength-swept system

We present a wavelength-swept coherent anti-Stokes Raman scattering (WS-CARS) spectroscopy system for hyperspectral imaging in thick tissue. We use a strategy where the Raman lines are excited sequentially, circumventing the need for a spectrometer. This fibre laser system, consisting of a pump laser synchronized with a rapidly tunable programmable laser (PL), can access Raman lines over a significant fraction of the high wavenumber region (2700–2950 cm−1) at rates of up to 10,000 spectral points per second. To demonstrate its capabilities, we have acquired WS-CARS spectra of several samples as well as images and hyperspectral images (HSI) of thick tissue both in forward and epi-detection. This instrument should be especially useful in providing local biochemical information with surrounding context supplied by imaging.

Dynamics of parabolic pulses in an ultrafast fiber laser

We report experimental and numerical results on the dynamics and propagation of parabolic pulses in a passively mode-locked ytterbium-doped fiber laser. Experimental data and numerical simulations are shown to match. Particular importance is attached to the pulse-shaping process in the different sections of the resonator. The paramount role of the gain fiber and saturable absorber in the laser is explicated.

Transient regime in a nth-order cascaded CW Raman fiber laser.

The transient regime of a nth-order CW Raman fiber laser is simulated from switch-on to the steady-state and from the steady-state to switch-off. The Stokes waves exhibit high-power spikes during the switch-on transition. We find that the high order Stokes fields reach steady-state faster than the low order ones and the pump.

Nonlinear pulse propagation in optical fibers using second order moments

We present simple yet efficient formulae for the propagation of the second order moments of a pulse in a nonlinear and dispersive optical fiber over many dispersion and nonlinear lengths. The propagation of the temporal and spectral widths, chirp and power of pulses are very precisely approximated and quickly calculated in both dispersion regimes as long as the pulses are not high order solitons.

Theoretical analysis of nth-order cascaded continuous-wave Raman fiber lasers. I. Model and resolution

We develop an approximate analytical solution to the steady-state equations that describe a nested fiber, Raman laser cavity that incorporates Bragg reflectors. From this solution the output power, the threshold power, and the efficiency are found. Numerical simulation of a six-step cascade shows that the approximate analytical solution is accurate within 1.5%. It appears that the laser behaves differently depending on whether it has an even or odd number of Stokes waves.

Programmable lasers: design and applications

A rapidly tunable, electronically controlled, pulse duration adjustable, arbitrarily programmable wavelength, picosecond mode-locked fiber laser is presented. The laser is tunable over 80 nm with sweeping frequency over 10 million wavelengths per second. The user can select from a preset linear sweep in either wavelength or optical frequency (kspace) or a custom (user-defined) sweep. Pulse duration is adjustable over tens of picoseconds with nearly Fourier limited linewidth. The laser can be harmonically mode-locked over 1 GHz. The average power is again fully programmable and is at least 50 mW, Watt level is possible with a high power amplifier. The output is a single mode polarization maintaining fiber. The laser possesses several external triggers, such as one trigger per optical pulse, one delayed trigger per optical pulse to synchronize with the experiments, one at the beginning when the laser is ready to sweep to start the data acquisition and one for each consecutive sweep, and finally one trigger for each wavelength change. Such a laser is so versatile that it can be used for medical imaging, material machining and nonlinear optics. It proves also a valuable research tool since all the parameters are adjustable.

Theoretical analysis of nth-order cascaded continuous-wave Raman fiber lasers. II. Optimization and design rules

Using the analytical model we developed for an nth-order cascaded Raman laser, we find the design rules for such lasers. We determine analytical expressions for the cavity length and the output-coupler reflectivity that maximize the output power and minimize threshold power. Simple expressions are obtained in the depleted-pump approximation. Deviations from these expressions when the pump is not completely depleted are shown to be different depending on the parity of the number n of Stokes shifts (cascades). The design rules show that the mirror reflectivity is a critical factor in the laser quality and that the ultimate slope efficiency epsilon is found to be g_n/g_0. We also find a condition to determine if P-doped fibers are more useful than Ge-doped fibers in Raman fiber lasers based only on the Raman shift and absorption of the fibers.

Tailoring wavelength sweep for SS-OCT with a programmable picosecond laser

This paper presents a unique and novel picosecond laser source that offers complete tailoring of the wavelength sweep and that benefits swept-source optical coherence tomography (SS-OCT) applications. Along with the advantages of a fiber-based architecture, the source is a fully programmable, electronically controlled actively mode-locked laser capable of rapidly tuning the wavelength and pulse characteristics. Furthermore, several sweep modes and configurations are available which can be defined by range, with linear sweeps in wavelength or k-space, or by arbitrary wavelengths. The source design is discussed and its use in SS-OCT with a prototype using a semiconductor optical amplifier as a gain medium is illustrated.

Picosecond programmable laser sweeping over 50 mega-wavelengths per second

We report here the successful realization of 25 millions wavelengths per second using an SOA based PL around 1565 nm at a 75 MHz repetition rate. The laser is simply composed of an SOA, a CFBG (10 ps/nm) with a 100 nm bandwidth, an optical circulator, an EOM (intensity modulator), and an output coupler (20%). Pulse duration is around 45 ps and OSNR of the pulse is around 35 dB at 1565 nm without sweeping. Tunable dispersion compensating module (TDCM) was used to compress the chirped pulse output and 10 ps pulse duration was obtained at 1548 nm. Finally 25 megawavelengths per second was realized with under 3 pulses per wavelength and 1024 discrete wavelengths. Linear k-space sweeping function was enabled in the swept-source OCT (SS-OCT) system through graphical user interface (GUI).

An Experimentally Validated Discrete Model for Dispersion-Tuned Actively Mode-Locked Lasers

In this paper, we present a new discrete model describing the steady-state characteristics of dispersion-tuned actively mode-locked fiber lasers pulses after each component in the cavity. The model was developed to perfect the design and further the knowledge of the capabilities of such lasers. The discrete model is compared to the traditional average model that is shown to be a limit case of the former. Several laser cavities were then built, with laser parameters changing over 4 order of magnitudes, in order to validate both models with experimental data. Both models show excellent agreement with the experimental data. Design considerations and limitations are then discussed in the light of this new model.