Pump Power Control Research Articles

Pump power control of photon statistics in a nanowire quantum dot

Pump power control of photon statistics in a nanowire quantum dot

Influence of the Doppler effect of a periodically moving mirror on the carrier-envelope frequency of a pulse train.

We investigate the influence of the optical Doppler effect on the carrier-envelope frequency (CEF) of a mode-locked pulse train. The laser pulses are Doppler-shifted in frequency during reflection off a periodically moving mirror that is driven by an electro-dynamical exciter inside an f-2f interferometer. Depending on the relative movement of the mirror at the instant of reflection, we experimentally demonstrate a CEF shift of the laser pulses up to ±69 kHz, which is sufficient for the carrier-envelope phase control of laser amplifiers with repetition rates of 10kHz and beyond. Using piezoelectric thick films, we show that the scheme also appears to be adaptable to the megahertz repetition rates of typical oscillators. As the phase control is exerted extra-cavity, Doppler-induced CEF modulation is virtually free of any side effects of traditional stabilization schemes that typically act on the pump power. Finally, the Doppler scheme may overcome servo loop bandwidth limitations associated with pump power control.

Radiation-Resistant Er3+-Doped Superfluorescent Fiber Sources.

The radiation effects of three Er3+-doped superfluorescent fiber sources (SFSs), which are based on three segments of Er-doped fibers with different lengths, are studied experimentally. We observed that the radiation-induced attenuation of the signal light of the 1530 nm band for an SFS is less than that of the 1560 nm band. Thus, the trimming technique of the Gauss-like spectra is investigated to reduce the mean wavelength drift. A filter was customized and used in superfluorescent fiber sources. To further reduce output power loss, the method with feedback control of pump power was adopted in the SFS. Then, the trimming spectral SFS with pump feedback control was tested under irradiation environment at the dose rate of 2.988 Gy/h. The experimental results demonstrate that the mean wavelength drift is <40 ppm and the loss of output power is <0.2 dB under a total dose higher than 1000 Gy. These findings confirm the significance of the method in improving radiation-resistant capabilities of fiber sources under irradiation environments.

Coherent beam combining and noise analysis of a colliding pulse modelocked VECSEL.

Optically-pumped SESAM-modelocked semiconductor disk lasers have become interesting ultrafast lasers with gigahertz pulse repetition rates, high average power and adjustable lasing wavelength. It is well established that colliding pulse modelocking (CPM) can generate both shorter pulses and improved stability. These improvements however typically come at the expense of a more complex ring cavity and two output beams. So far similar modelocking results have been obtained with CPM vertical external-cavity surface-emitting lasers (VECSELs) and with SESAM-modelocked VECSELs or modelocked integrated external-cavity surface-emitting lasers (MIXSELs) in a linear cavity. However coherent beam combining of the two output beams of a CPM VECSEL could result in a significantly higher peak power. This is interesting for example for applications in biomedical microscopy and frequency metrology. Here we demonstrate with a more detailed noise analysis that for both output beams of a CPM VECSEL the pulse repetition rates and the carrier envelope offset frequencies are locked to each other. In contrast to standard SESAM-modelocked VECSELs in a linear cavity, we only have been able to actively stabilize the pulse repetition rate of the CPM VECSEL by cavity length control and not by pump-power control. Furthermore, a first coherent beam combining experiment of the two output beams is demonstrated.

Pressure Pump Power Control in the Primary Circuit of the Heat Exchange System

In this paper we consider the problem of speed in hot water systems where highly efficient plate heat exchanger is used. Especially marked the problem which is connected with long transition drive of constant speed exceeding the time of the heat exchanger accumulative tank emptying more than twice. As a regulating element in the heat exchange system there was proposed to use asynchronous electric drive of pressure pump in the primary circuit of the heat exchanger. For correct use of such electric drive we solved the problem of control object mathematical model synthesis, which has non-linear properties, in particular, the transfer coefficient of the circuit can vary in more than 6 times. At the same time there was revealed the dependence of the transfer coefficient on the motor speed, which must be considered in the controller synthesis. In conclusion we suggested the solutions of regulators synthesis tasks with customizable settings for speed and switchable structure between relay λ and PI regulators.

Feedforward control techniques for Erbium–doped fiber amplifiers — challenges and solutions

Feedforward control of optical amplifiers is mandatory in wavelength routed networks to avoid traffic interruption resulting from fast input power variations. Effects limiting the efficiency of this control technique are discussed and an overview over techniques compensating for the most important ones is presented. Detailed insight into the wavelength dependence of the optimum pump power setting is provided by a mathematical model. Taking this dependence into account requires to filter the input signal. Three different techniques are explained that make use either of an additional filter placed in front of the input monitor, an embedded gain–flattening filter, or even the erbium–doped fiber itself. Timing is another important issue. Besides introducing a delay in front of the first doped fiber, sophisticated control schemes working without additional optical components by modifying the waveform of the pump signal are analyzed. Different setups such as cascaded amplifier stages with intermediate dispersion compensating fiber are considered. The stages are either controlled individually or are coupled via a pump splitter. Finally, solutions complementing the pump power control by fast adaptation of the attenuation of a variable attenuator are contemplated.

All-fiber coherent beam combining with phase stabilization via differential pump power control

Coherent beam combining enables power scaling beyond the limits of single amplifiers. Therefore, improving the performance and simplicity of coherent combination techniques is of great interest for many high power applications. Here, we show all-fiber coherent beam combining of two ytterbium doped amplifiers with and without a dedicated phase actuator and a total output power up to 25 W. Instead of a dedicated phase actuator, we directly controlled the two ytterbium amplifiers to also stabilize their relative phase. We compared the performance of this method with phase stabilization using two piezo driven fiber stretchers. In both cases, power noise was dominated by the single amplifier.

Compensating unflattened WDM chips spectra using dynamic backward-pumped fiber Raman amplifiers technology

Fiber Raman amplifiers (FRAs) with multiple pumps are proposed to realize dynamic gain equalization for a spectral chips signal with a non-flattened broadband light source (BLS) in a spectrum-sliced wavelength-division multiplexing (WDM) network. In FRAs with multiple pumps, the gain profile can be adjusted via appropriate specification of the relative position of the pump wavelengths and the power of the pump waves. This paper combines a pump-power control algorithm and a genetic algorithm (GA) to establish the optimal pump spectrum for any specified gain spectrum in the WDM system. The method flattens the power spectra of WDM chips by identifying the optimal pump wavelengths and pump power of backward-pumped FRAs. It avoids the conventional requirement for time-consuming trial-and-error adjustments or intensive numerical simulations. Simulation results show that the scheme is simple, effective, and applicable for various BLSs in a spectrum-sliced WDM transmitter.

Effect of pump power on the tuning range of a filterless erbium-doped fiber ring laser

In this paper, we establish the influence of pump power on the tuning characteristics of a filterless erbium-doped fiber laser, operating in the L band. Tunable action is achieved with the control of intra cavity loss. The explicit dependence of tunability on the average inversion levels is brought out. The shift in the lower limit of tuning range and the non-linear dependence of lasing wavelength on the intra cavity loss are analytically deduced using the gain spectra and experimentally interpreted using amplified spontaneous emission spectra. Continuous tunability is achieved with the careful control of pump power.

Frequency stabilization of mode-locked Erbium fiber lasers using pump power control

Mode-locked erbium fiber lasers can serve as frequency comb generators in the 1.5 μm telecommunication band or as frequency dividers generating low noise pulse trains at microwave repetition rates from a visible or near infrared frequency standard. Such applications require suitable stabilization methods both for the laser’s carrier frequency and the pulse repetition frequency. While control of the optical resonator length with the help of a piezo actuator is an obvious method, we investigate in this paper frequency stabilization of the fiber laser via pump power control. Using this method, we stabilize the pulse repetition rate of the Er:fiber-laser with respect to a hydrogen-maser with residual averaged timing errors of a few femtoseconds (for averaging times between one and one hundred seconds), an order of magnitude below the timing noise of the maser itself.

Modelling of a pump-power-controlled gain-locking system for multi-pump wideband Raman fibre amplifiers

Transient gain response of optical amplifiers to the addition/removal of channels is a major problem in multi-wavelength amplified optical networks. In order to avoid error bursts in the surviving channels, signal power fluctuations due to channel addition or removal caused by network reconfigurations or line failures must be minimised. The authors analyse the recently proposed and experimentally tested gain-locking technique for Raman fibre amplifiers, based on surviving channel power monitoring and pump power control. The analysis is based on the application of a comprehensive large-signal numerical model, which incorporates temporal properties and downstream propagation of multiple signals, upstream propagation of multiple pumps and downstream and upstream propagation of amplified spontaneous emission (ASE) spectral components in a Raman fibre amplifier. It follows from the theoretical investigation that the peak-to-peak surviving channel power excursion can be reduced to less than 0.2 dB for the addition/removal of 50% of channels when the pump power feedback parameters are appropriately selected.

A channel-number insensitive erbium-doped fiber amplifier with automatic gain and power regulation function

The design scheme for an erbium-doped fiber amplifier (EDFA) with automatic channel-by-channel gain and power regulation function is discussed with much emphasis on the pump power control scheme and the requirement for feedback circuitry. Based on both wavelength and time-resolved simulation technique, an amplifier repeater employing novel high-speed automatic gain control (AGC) and automatic level control (ALC) functions is designed and implemented. The AGC and ALC scheme can suppress the transient power fluctuation of a surviving channel caused by adding or dropping all other channels less than 0.45 dB and keep output power constant over 9-dB input power range.