We report the current progress in the development of a compact, deployable cold-atom interferometry sensor platform towards atomic sensors for position, navigation, and time (PNT) applications. A simplified atomic sensor head with diffractive optics, an alignment-free optical package, and photonic-integrated-circuit (PIC) compatible laser architecture [1] are essential for its compactness and deployability. This cold-atom sensor platform can be generally applied to gravimeters, accelerometers, gyroscopes, and clocks, and the sensor platform includes significant engineering efforts in the development of grating-mirror magneto-optical traps (G-MOTs), custom titanium vacuum package with passive pumping, and silicon photonics multi-channel on-chip single sideband modulators.
We report an all-fiber passively Q-switched laser using a large mode area (LMA) Yb3+ -doped fiber claddingpumped at 915 nm and an unpumped single-mode (SM) Yb3+-doped fiber as the saturable absorber (SA). The saturable absorber SM fiber and LMA gain fiber were coupled with a fiber taper designed to match the fundamental spatial mode of the LMA fiber and the expanded LP01 mode of the single mode fiber. The amplified spontaneous (ASE) intensity propagating in the single mode SA saturates the absorption before the onset of gain depletion in the pumped fiber, switching the fiber cavity to a high Q-state and producing a pulse. Using this scheme we demonstrate a Q-switched all-fiber oscillator with 32 μJ 93 ns pulses at 1030 nm. The associated peak power is nearly two orders of magnitude larger than that reported in previous experimental studies using a single Yb+3 saturable absorber fiber. The pulse energy was amplified to 0.230 mJ using an Yb3+-doped cladding pumped fiber amplifier fusion spliced to the fiber oscillator, increasing the energy by eight fold while preserving the all-fiber architecture.
We report a passively Q-switched all-fiber laser using a large mode area (LMA) Yb3+-doped fiber cladding-pumped at 915 nm and an unpumped single-mode Yb3+-doped fiber as the saturable absorber (SA). The saturable absorber and gain fibers were first coupled with a free-space telescope to better study the composite system, and then fusion spliced with fiber tapers to match the mode field diameters. ASE generated in the LMA gain fiber preferentially bleaches the SA fiber before depleting the gain, thereby causing the SA fiber to act as a passive saturable absorber. Using this scheme we first demonstrate a Q-switched oscillator with 40 μJ 79 ns pulses at 1026 nm using a free-space taper, and show that pulses can be generated from 1020 nm to 1040 nm. We scale the pulse energy to 0.40 mJ using an Yb3+-doped cladding pumped fiber amplifier. Experimental studies in which the saturable absorber length, pump times, and wavelengths are independently varied reveal the impact of these parameters on laser performance. Finally, we demonstrate 60 μJ 81 ns pulses at 1030 nm in an all fiber architecture using tapered mode field adaptors to match the mode filed diameters of the gain and SA fibers.
Fiber dispersion plays a significant role in spectral broadening of incoherent continuous-wave light. We develop a self-consistent stochastic model for spectral broadening of incoherent continuous-wave light through nonlinear wave mixing and apply this model to numerical simulations of spectral broadening in a continuous-wave fiber Raman laser. The results of these numerical simulations agree very well with carefully conducted laboratory measurements. Under a wide range of operating conditions, these numerical simulations also exhibit striking features, such as damped oscillatory spectral broadening (during the initial stages of propagation) and eventual convergence to a stationary, steady-state spectral distribution at sufficiently long propagation distances. We analyze the important role of fiber dispersion in such phenomena. We also derive an analytical rate equation expression for spectral broadening, whose numerical evaluation is far less computationally intensive than the fully stochastic simulation, and a mathematical criterion for the applicability of this analytical expression.
We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm.
We discuss the dramatic development of high-power fiber laser technology in recent years and the prospects of kilowattclass
single-frequency fiber sources. We describe experimental results from an ytterbium-doped fiber-based multihundred-watt single-frequency, single-mode, plane-polarized master-oscillator power amplifier (MOPA) operating at 1060 nm and a similar source with 0.5 kW of output power, albeit with a degraded beam quality (M2 = 1.6) and not linearly polarized. Experiments and simulations aimed at predicting the Brillouin limit of single-frequency system with a
thermally broadened Brillouin gain are presented. These suggest that single-frequency MOPAs with over 1 kW of output power are possible. In addition, the power scalability of a simple single-strand fiber laser to 10 kW is discussed.
We demonstrate a sub-100 fs frequency doubled fiber laser operating at 810 nm. The laser produces 60 mW of average power at a repetition rate of 50 MHz. Extremely low amplitude noise (below 0.1%) and compact size makes this source ideal replacement for low power ultrafast Ti:Spphire lasers.
We demonstrate a high power erbium-ytterbium co-doped large-core fiber laser with narrow linewidth, an M2 value of 1.7 and a broad tuning range. The fiber was cladding-pumped by a diode stack emitting at 975 nm. The laser had a linewidth around 0.16 nm and was tuned from 1533 nm to 1566 nm by compression-tuning a fiber Bragg grating. Output powers in excess of 30 W were obtained over the entire laser tuning range which was limited by the low gain at wavelengths shorter than 1533 nm and by the grating fabrication wavelength at 1566 nm. The laser slope efficiency was ~30% and the threshold ~3.3 W. Our results underline the capability for efficient, broad-band, high-power operation of large-core Er-Yb doped fibers and demonstrate compatibility with telecom components like standard single-mode fibers and fiber Bragg gratings.
A 978 nm Yb-doped jacketed-air-clad fiber MOPA generates 18 mW of power at 488.7 nm when single-pass frequency-doubled in periodically poled KTP at room temperature. The tunable fiber laser - fiber amplifier MOPA provided 2.7 W of output power at 978 nm.
We report for the first time, more than 400 mW of output power at 1056.1nm from a distributed feedback (DFB) fiber laser. The DFB fiber laser comprises a simple π-phase-shifted Bragg grating written into a photosensitive ytterbium-doped fiber. The laser operates with a single longitudinal mode at a wavelength defined by the phase shift and the grating period. Without any internal polarisation selection mechanism, the cavity supports orthogonal polarisation modes, which operate simultaneously. The DFB fiber laser was pumped by a 976nm amplified spontaneous emission (ASE) source based on a ytterbium doped jacketed air clad (JAC) fiber pumped by a 915nm multimode laser diode source. An output of 400mW at 1056.1nm was obtained from the output port while 70mW was obtained from the other port, when pumped with 1.5W of 976nm radiation. The total output from the DFB fiber laser was approximately linear with increasing pump power and the overall performance was limited by the available pump power. The spectral characteristics and signal to noise ratio remained similar over the pump power range. The output of the DFB was in single-mode fiber (ie. M2~1).
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