The design and performance of a compact laser system for autonomous cooling of rubidium atoms in a small Cube-Sat satellite is described. The laser system is suitable for use in cold atom interferometers that are deployed in space for accurate observation of earth’s gravity and magnetic fields and detection of tectonic changes. The laser system features a frequency doubled DFB laser and erbium doped amplifier, which is mainly fabricated from telecommunications qualified components with proven high reliability. The laser has an output power of greater than 75mW with a sub-MHz linewidth and a tuning range of greater than 300GHz. The laser and drive electronics fit into a 200mm x 100mm x 30mm package and have a mass of less than 1kg. On-board the CubeSat the laser has been used to demonstrate atom cooling and to autonomously acquire and lock to the magneto-optical trap using feedback from the cold Rb-atom fluorescence to control the dfb laser frequency. The complete cube-sat has passed vibration tests for rocket launched conditions.
Cold atom interferometers are emerging as important tools for metrology. Designed into gravimeters they can measure extremely small changes in the local gravitational field strength and be used for underground surveying to detect buried utilities, mineshafts and sinkholes prior to civil works. To create a cold atom interferometer narrow linewidth, frequency stabilised lasers are required to cool the atoms and to setup and measure the atom interferometer. These lasers are commonly either GaAs diodes, Ti Sapphire lasers or frequency doubled InGaAsP diodes and fibre lasers. The InGaAsP DFB lasers are attractive because they are very reliable, mass-produced, frequency controlled by injection current and simply amplified to high powers with fibre amplifiers. In this paper a laser system suitable for Rb atom cooling, based on a 1560nm DFB laser and erbium doped fibre amplifier, is described. The laser output is frequency doubled with fibre coupled periodically poled LiNbO3 to a wavelength of 780nm. The output power exceeds 1 W at 780nm. The laser is stabilised at 1560nm against a fibre Bragg resonator that is passively temperature compensated. Frequency tuning over a range of 1 GHz is achieved by locking the laser to sidebands of the resonator that are generated by a phase modulator. This laser design is attractive for field deployable rugged systems because it uses all fibre coupled components with long term proven reliability.
In this paper, an overview of the EU FP7 project ISLA (Integrated disruptive componentS for 2 μm fibre Lasers) is given. The aim of ISLA was to develop a set of “building block” components and a “tool-kit” of processes to define an integrated modular common platform for two micron fibre lasers consisting of compatible and self-consistent active and passive fibres, fused fibre couplers and combiners, fibre-coupled isolators, modulators and high power pump laser diodes. We also present results from our work on developing passive components for 2 μm fibre lasers. This includes high power pump combiners that have been tested up to 0.5 kW and combiners for in-band pumping of holmium lasers. Couplers for use as splitters, power monitors and wavelength division multiplexers have also been demonstrated. Wideband couplers, with a coupling ratio that only varies ± 12% over 400 nm, have also been developed to exploit the wide tuning range possible with thulium fibre lasers. Research into different isolator materials was also conducted to find materials with large Verdet constants to be used in 2 μm isolators. Fibre-coupled isolators were then manufactured using a selection of these materials. Isolators that had insertion losses of < 1 dB and isolation of > 35 dB were demonstrated using PM and non-PM fibres. In the PM isolators, PER > 23 dB was achieved.
We present results from an all-fibre thulium laser system that can be tuned to any wavelength between 1710 – 2110 nm, without using any moving mechanical parts. An Acousto-Optic Tunable Filter (AOTF) is used as the tuning element, which allows for the wavelength to be tuned in ~ 20 μs. Core-pumped and cladding pumped thulium fibres are used to enable lasing action across the wavelength range. We use in-house fabricated fused fibre couplers and combiners that have a flattened coupling response with wavelength to allow for the system to be built in an all fibre design. These couplers have a coupling response that only varies by +/- 10% over the 400 nm operating range. The laser can output powers between 1-5 mW over 1710 – 2110 nm and has a linewidth of <0.2 nm. An Acousto-optic modulator is used as a switch on the output of the laser to switch the signal between core-pumped and cladding-pumped amplifier stages. This allows for the output signals to be amplified to ~1W levels.
Second harmonic generation (SHG) is a ubiquitous technique for extending the spectral coverage of laser sources into regions that would otherwise be technologically challenging to access. SHG schemes typically rely on the use of bulk optical components, resulting in systems with large footprints requiring precise optical alignment. Integration of the SHG components into a single unit facilitates the implementation of compact, robust and turn-key sources, suitable for applications in biophotonic imaging, amongst others. We report on the development of fiber-coupled frequency doubling modules and their application to novel fiberintegrated picosecond pulse sources in the visible and near-visible. The modules employ a simple, single-pass configuration using a periodically-poled lithium niobate (PPLN) crystal as the nonlinear conversion medium. They are readily adaptable for different fiber pump laser configurations and are configurable with either fiber-coupled or collimated free-space outputs. Two sources using the modules are presented, operating at 780 nm and 560 nm. The 780 nm source utilizes an erbium master oscillator power fiber amplifier (MOPFA) scheme. SHG was performed in a 35 mm long crystal, generating 3.5 W of 780 nm radiation with a pulse duration of 410 ps at 50 MHz and conversion efficiencies exceeding 20%. Results of this source being used for parametric wavelength conversion in photonic crystal fiber are discussed. The 560 nm source was based on SHG of a Raman amplified CW diode pumped by a pulsed ytterbium-fiber MOPFA. This source generated 450 mW of average power with conversion efficiencies greater than 20%.
We report on the development and testing of optical isolators for use in 2-micron fiber laser systems. A variety of potential Faraday rotator materials were characterised to identify the most suitable materials for use in the 1700-2100nm wavelength range. Isolators based on the three best performing materials were then developed and packaged as fiber-in, fiber-out and fiber-in, beam-out devices. The isolators were then tested in CW, pulsed and ultrafast laser systems. The three different designs produced different performance characteristics, but all designs demonstrated isolation >25dB and insertion losses of <1.2 dB.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.