ABSTRACT
Wavelength information is essential for any researcher in optics and photonics, and for this reason, a wide range of devices is available for measuring it. However, the techniques available today are limited either to a resolution of nanometers or a measurement rate of kHz. In this paper, we present a simple but highly versatile technique based on second-harmonic generation to measure fast wavelength dynamics of laser diodes. We demonstrate a resolution of 0.7 pm and a measurement rate in the MHz range. The measurement rate is limited only by the photodetector, and the wavelength resolution is limited mainly by the length of the nonlinear crystal and the noise of the detectors. The technique can, e.g., be used to investigate the mode-hop behavior of laser diodes during pulsed operation. To demonstrate this, we show the wavelength changes of a laser diode during a single pulse.
ABSTRACT
Power modulated visible lasers are interesting for a number of applications within areas such as laser displays and medical laser treatments. In this paper, we present a system for modulating the second-harmonic light generated by single-pass frequency doubling of a distributed feedback (DFB) master oscillator power amplifier (MOPA) laser diode with separate electrical contacts for the MO and the PA. A modulation depth in excess of 97% from 0.1 Hz to 10 kHz is demonstrated. This is done by wavelength tuning of the laser diode using only a 40 mA adjustment of the current through the MO. The bandwidth of the modulation is limited by the electronics. This method has the potential to decrease the size as well as cost of modulated visible lasers. The achievable optical powers will increase as DFB MOPAs are further developed.
ABSTRACT
We demonstrate a novel imaging fiber bundle ("hexabundle") that is suitable for low-light applications in astronomy. The most successful survey instruments at optical-infrared wavelengths use hundreds to thousands of multimode fibers fed to one or more spectrographs. Since most celestial sources are spatially extended on the celestial sphere, a hexabundle provides spectroscopic information at many distinct locations across the source. We discuss two varieties of hexabundles: (i) lightly fused, closely packed, circular cores; (ii) heavily fused non-circular cores with higher fill fractions. In both cases, we find the important result that the cladding can be reduced to ~2 µm over the short fuse length, well below the conventional ~10λ thickness employed more generally, with a consequent gain in fill factor. Over the coming decade, it is to be expected that fiber-based instruments will be upgraded with hexabundles in order to increase the spatial multiplex capability by two or more orders of magnitude.
Subject(s)
Astronomy/instrumentation , Fiber Optic Technology/instrumentation , Image Enhancement/instrumentation , Equipment Design , Equipment Failure AnalysisABSTRACT
We demonstrate the fabrication of a high performance multi-mode (MM) to single-mode (SM) splitter or "photonic lantern", first described by Leon-Saval et al. (2005). Our photonic lantern is a solid all-glass version, and we show experimentally that this device can be used to achieve efficient and reversible coupling between a MM fiber and a number of SM fibers, when perfectly matched launch conditions into the MM fiber are ensured. The fabricated photonic lantern has a coupling loss for a MM to SM tapered transition of only 0.32 dB which proves the feasibility of the technology.