Pump Power Variation Research Articles

Stable L-band superfluorescent fiber source using one pump

We first demonstrate that by inserting an appropriate section of unpumped erbium-doped fiber (EDF) in an erbium-doped superfluorescent fiber source (SFS) of double-pass backward configuration, a stable L-band SFS can be achieved. The fiber-length arrangement of unpumped fiber are shown to have significant effects on the output properties of the L-band SFS. The spectral linewidth is broadened, and the variation of mean wavelength versus pump power is eliminated to achieve a wideband and mean wavelength stable L-band SFS by optimizing the fiber-length ratio of the pumped fiber length to the total fiber length. For a 19-m-long total EDF with fiber-length ratio of 0.84, a mean wavelength stable L-band SFS with a spectral linewidth of 49.6 nm, an output power of 46.3 mW, and a mean wavelength of 1583.20 nm was experimentally achieved.

Stabilized soliton self-frequency shift and 0.1- PHz sideband generation in a photonic-crystal fiber with an air-hole-modified core

Fiber dispersion and nonlinearity management strategy based on a modification of a photonic-crystal fiber (PCF) core with an air hole is shown to facilitate optimization of PCF components for a stable soliton frequency shift and subpetahertz sideband generation through four-wave mixing. Spectral recoil of an optical soliton by a red-shifted dispersive wave, generated through a soliton instability induced by high-order fiber dispersion, is shown to stabilize the soliton self-frequency shift in a highly nonlinear PCF with an air-hole-modified core relative to pump power variations. A fiber with a 2.3-microm-diameter core modified with a 0.9-microm-diameter air hole is used to demonstrate a robust soliton self-frequency shift of unamplified 50-fs Ti: sapphire laser pulses to a central wavelength of about 960 nm, which remains insensitive to variations in the pump pulse energy within the range from 60 to at least 100 pJ. In this regime of frequency shifting, intense high- and low-frequency branches of dispersive wave radiation are simultaneously observed in the spectrum of PCF output. An air-hole-modified-core PCF with appropriate dispersion and nonlinearity parameters is shown to provide efficient four-wave mixing, giving rise to Stokes and anti-Stokes sidebands whose frequency shift relative to the pump wavelength falls within the subpetahertz range, thus offering an attractive source for nonlinear Raman microspectroscopy.

A passively mode-locked fiber laser at 1.54 μm with a fundamental repetition frequency reaching 2 GHz

We demonstrate a fundamentally mode-locked fiber laser with a repetition frequency in excess of 2 GHz at a central wavelength of 1.535 mum. Co-doped ytterbium-erbium fiber provides the gain medium for the laser, affording high gain per unit length, while a semiconductor saturable absorber mirror (SAM) provides the pulse shaping mechanism in a standing wave cavity. Results are shown confirming cw mode-locking for 1 GHz and 2 GHz repetition frequency systems. The response of the frequency comb output to pump power variations is shown to follow a single pole response. The timing jitter of a 540MHz repetition-rate laser has been suppressed to below 100 fs through phase-lead compensated feedback to the pump power. Alternatively, a single comb line of a 850MHz repetition-rate laser has been phase-locked to a narrow linewidth cw laser with an in-loop phase jitter of 0.06 rad(2). The laser design is compatible with low-noise oscillator applications.

Efficient Yb3+:Y3Al5O12 ceramic microchip lasers

Low-threshold and highly efficient continuous-wave (cw) Yb3+:Y3Al5O12 (Yb:YAG) ceramic laser with near-diffraction-limited beam quality was demonstrated at room temperature. Dual-wavelength operation at 1030 and 1049nm with 5% transmission of the output coupler was achieved by varying pump power intensity. Slope efficiencies of 79% at 1030nm and 67% at 1049nm were achieved for 1-mm-thick Yb:YAG ceramic plate (CYb=9.8at.%) under cw laser-diode pumping. The effect of pump power on the laser emission spectra of both wavelengths is addressed. Excellent laser performance indicates that Yb:YAG ceramic laser materials could be potentially used in high-power solid-state lasers.

Optical filtering and switching using counter-propagating wavelength converter

A high-efficiency optical filter, based on a counter-propagating wavelength converter in ZnTe, is theoretically demonstrated. The filter has extremely narrow bandwidth of 0.5 A corresponding to pump 0.3 W power and 1 cm length of quasi-phase-matching (QPM) grating, tunable over several nanometers of bandwidth by combination of the grating length and pump power variation. The presented scheme is also a candidate for a wavelength-dependant switch.

Theory of Kerr-lens mode locking: role of self-focusing and radially varying gain

The ABCD-matrix formalism is generalized for the description of self-focusing and radially varying pump power in a nonparabolic approximation. This extended formalism is used for the investigation of the operation and for the optimization of the saturable aperture loss, the power-dependent average gain, and the resonator magnification of Kerr-lens mode-locked lasers with as well as without an internal aperture. The calculated amplitude modulation parameters are compared with the necessary condition for self-starting and for the shortest possible pulse duration limit.

Quantum limited noise figure operation of high gain erbium doped fiber amplifiers

Performance improvements obtained by using an isolator as an amplified-spontaneous-emission-suppressing component within erbium-doped fibers are evaluated. Simultaneous high-gain and near-quantum-limited noise figures can be obtained by such a scheme. The noise figure improves for input signal powers below -5 dBm, and an improvement of 2.0 dB with a simultaneous gain increase of 4.1 dB is measured relative to a gain-optimized fiber. The optimum isolator location is evaluated for different pump and signal wavelengths in both an Al/Er-doped and a Ge/Er-doped fiber, for pump and signal power variations and different pump configurations. In all cases the optimum isolator position lies within 10-37% of the total fiber length for small signal operation. >

Stability of a 500 km erbium-doped fiber amplifier cascade

The stability of a cascade system of erbium-doped fiber amplifiers, due to pump and signal power variations, has been examined by use of a very accurate model. Even with an automatic gain control loop included, a fallout of a pump laser in the first inline amplifier is shown to produce a more than seven times as high increase of the bit error rate then for the fallout of other amplifier pumps, showing that the fallout of the forward pump is by far the most critical. The stability to simultaneous changes in pump and signal power is examined and can be increased remarkably insertion of an additional amplifier.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

LED end-pumped Nd:YAG lasers

Experimental results are reported on the room-temperature operation of Nd:YAG lasers end pumped with an LED. The radiation from a 10-percent-efficient 0.46-mm-diam domed LED was coupled to the end of a 0.46-mm-diam × 5.0-mm-long laser rod with a large hemispherical reflector. At 20°C, a multimode laser power of 0.25 mW was obtained at an LED current of 250 mA. By measuring the variation of threshold pump power with rod temperature and the laser power versus pump power just above threshold, both the laser cavity loss and the output mirror transmission were determined. A round-trip cavity loss as low as 0.022 percent was measured. A calculation of the fractional pump power absorbed in the rod for the LED spectrum gave 56 percent for a 5-mm-long rod while measurements showed that 30 to 35 percent of the LED power was being absorbed indicating an LED-to-laser rod coupling efficiency of 54 to 63 percent for this arrangement. With such efficient absorption of pump power and low cavity loss, end-pumped Nd:YAG lasers with high slope efficiencies above threshold are possible.

A theory of self-pulsing lasers

We demonstrate different operation states which can be switched by the polarization control in an erbium-doped fiber laser cavity with normal dispersion, including passive single-pulse and multiple-pulse mode-locking, coherent pulse pattern, and passive Q-switching. The mode-locked single pulse has a smooth and broad rectangular-shaped spectrum. With increasing pump power, multiple pulses appear and finally six pulses are observed, where the pulses have no interaction with each other. Keeping the pump power at 407 mW and adjusting the polarization state, we observe the coherent pulse pattern with the pulse numbers from 2 to 5. It is the first time five coherent pulses in the 1.55 μm normal dispersion cavity have been observed, to our knowledge. The mode-locked spectra are highly modulated and the largest pulse separation of 31.9 ps is observed for the two-pulse case. When the pump power exceeds 180 mW, the mode-locked operation can be switched to the passively Q-switched operation by controlling the polarization state. The repetition rate and pulse width can be changed by pump power variation, and the spectrum is tunable in the range of 8.45 nm.

Effect of Upper Sideband Impedance on a Lower Sideband Up-Converter

An analysis is given of a lower sideband up-converter which includes a finite circuit reactance X/sub 33/ at the upper sideband frequency, in addition to the circuit impedances at the input signal and output lower sideband frequencies. The expressions developed for the gain, gain sensitivity to pump power variation, and noise figure show the extent to which gain and gain sensitivity decrease, and noise figure increases when X/sub 33/ is finite, as compared to the case when X/sub 33/ is infinite. For a simple circuit configuration the gain-bandwidth product changes markedly when X/sub 33/ is small at the center frequency. In addition, when second-harmonic pump power is allowed to flow through the varactor diode, the performance of the lower sideband up-converter can be improved.

A NEW MODEL FOR THE TEMPERATURE-DEPENDENT CdS LASER

The temperature dependence of laser wavelength and threshold pump power of a CdS platelet laser operating from 2 to 240°K are presented. A model is proposed that demonstrates how the temperature dependence of band edge absorption determines the variation of laser wavelength and threshold pump power over this temperature range.

A ferromagnetic microwave amplifer with increased signal bandwidth

Previous work in ferromagnetic microwave amplification has followed a two-fold course of reducing the necessary pump power by 1) reducing the resonant absorption linewidth and 2) improving the filling factor of magnetic material to the resonant system. These developments have led to the Denton-type amplifier employing a parallel-pumped single crystal sphere of yttrium iron garnet operating in the magnetostatic mode where the pump power is, typically, 1/2 watt. However, the resultant narrow linewidth (or high Q of the resonant absorption) restricts the signal bandwidth to the order of 100 kc/s. This is a major limitation in most applications. This paper describes the multiple pumping process used to remove this limitation of the Denton amplifier. The resulting amplifier has a 2-Mc/s or greater signal bandwidth with the associated increase in gain-bandwidth product while total pump power remains less than one watt. The theory of operation is extended to cover the improved operational stability to temperature and pump power variations. A C-band (5.8 Gc/s) dielectrically loaded version of this amplifier using an X-band pump is described and performance details given.

A Series-Connected Traveling-Wave Parametric Amplifier (Correspondence)

The conventional parametric amplifier consisting of a single variable element with its accompanying resonant circuits is inherently a narrow-band device. Analysis has also shown that such amplifiers when operating at high gain are extremely sensitive to pump power, i.e., small variations in pump power lead to large variations in gain. Traveling-wave parametric amplifiers, in which not one but many variable elements are involved, have been designed or built to overcome the two limitations mentioned above. This paper is concerned with the analysis of one such amplifier in which the variable elements are placed in series with the signal line as opposed to one in which the elements are placed in shunt. In particular, the variable elements are capacitance diodes.