THORLABS PICO D, Руководство пользователя

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Figure 2–1 Schematic Radians PICO™. PICO is based on a Littrow resona-
tor. 1) Diffraction grating, 2) Intra-cavity collimating hybride (i.e.
refractive and diffractive combination) achromatic lens, 3) Laser
diode, 4) Output coupling optics including an isolator 5) Fiber op-
tics 6) Motor.
2.3 Basic operation.
PICO D is based on a patented low SSE Littrow external cavity laser geometry, c.f
Figure 2–1 . The intra-cavity lens collimates the light emitted from the laser diode be-
fore the beam impinges on the diffraction grating. Wavelength selectivity is achieved
by tilting the diffraction grating. The tilting is controlled by a patented moving coil
(“motor”) arrangement. The beam reflected from the diffraction grating is directed
back to the laser diode. Thus, the laser resonator cavity is formed between the dif-
fraction grating and the leftmost side of the laser diode as seen in Figure 2–1. The
output beam is collimated and sent through an optical isolator before the beam is
launched into the optical fiber.
Due to the analog interface PICO D is easy to integrate in the user’s system configu-
ration. The user supplies an analog signal to tune (sweep) the laser between the
minimum and maximum wavelengths defining the tuning range. The tuning of PICO
D is truly continuous. The output wavelength of the laser will follow the applied ana-
log signal. Furthermore, by applying a constant voltage to the tuning input, the laser
will lase at a fixed wavelength. This implies that the laser can randomly access any
fixed wavelength within the tuning range.
The control system continuously monitors the angular position and the angular
speed of the mechanical arm onto which the grating is mounted. The outputs are fed
to the internal control circuitry. The wavelength control system is designed to:
Follow a ramp ( i.e. wavelength vs . time signal) without errors with short settling
times
Clamp the laser at a fixed wavelength ( i.e. a fixed angular position of the grating
arm) without errors