有源耦合腔激光器锁模特性研究

本文在理论上首次发现有源耦合腔激光器的自启动锁模和时域调制特性,并对其进行了全面的分析和计算.对有源耦合腔激光器的自启动锁模机制和时域调制特性给予详尽的数值计算结果和清晰的物理图象解释,提出在有源耦合腔锁模激光器中可用连续泵浦源代替锁模泵浦源,而且有产生更短的光脉冲可能性.     

Mixed external cavity mode dynamics in a semiconductor laser

We observe experimentally and numerically novel mixed-mode dynamic states of a diode laser subject to two delayed optical feedbacks. These states have been proposed and analyzed within the framework of the Lang-Kobayashi single-feedback model. Such states are combinations of two distinct external cavity modes and can be identified through a characteristic sequence of a Hopf bifurcation followed by a secondary quasi-periodic bifurcation. We present experimental and numerical results that demonstrate such sequences.     

Slave-master dynamics of semiconductor laser with short external cavity

In this paper, the dynamical response of a slave semiconductor laser, with short cavity, under injection of a chaotic light from a master semiconductor laser has been widely studied. This is analyzed numerically via bifurcation diagrams, in terms of the phase and strength of the feedback, as control parameters. It is shown that, both of these parameters should be considered in the dynamical response of the slave laser. Our numerical calculations show that the dynamics of the slave laser imitates the master laser, in addition to the feedback strength, it also heavily depends on the injection dynamics and rates. Numerical results also show that for different values of the control parameters, the intensity of the slave laser output can be fully different from the injection source. However, we found out under appropriate conditions, that the dynamics of the slave can be the same as the master laser. The results also show that the output of the slave laser, compared to its output without injection, can be stabled in the appropriate values of the injection rate from the master laser.     

Modulation enhancement of a laser diode in an external cavity

The influence of Zn-atom additive on ‘pure’ copper vapor laser output characteristics is studied. The laser pulse width, energy and power are found to increase under the diffusion of zinc atoms from a zinc-containing reservoir into the discharge of the copper-vapor laser at temperatures above 500°C. Additional absorption experiments and calculations are consistent with the conclusion that not only optical resonant pumping by the 213.9-nm Zn I line, but also other processes, should be taken into account to explain the effects of additive influence.     

Power efficiency of a semiconductor laser with an external cavity

Optical feedback modifies the power vs. current diagram of a laser diode as well as its spectrum. Though optimization of the spectral characteristics is usually the main goal in the design of an external cavity source, power efficiency is also important, especially with relatively high power devices, where temperature variations due to dissipation can have an impact on the wavelength stability and on the laser lifetime. A useful parameter to describe the total power efficiency of the stabilized laser, relative to that of the solitary laser, is proposed in this paper. The dependence of this parameter on the characteristics of the active device, and of the external cavity, is investigated.     

Entanglement dynamics and decoherence of an atom coupled to a dissipative cavity field

In this paper, we investigate the entanglement dynamics anddecoherence in the interacting system of a strongly driventwo-level atom and a single mode vacuum field in the presence ofdissipation for the cavity field. Starting with an initial productstate with the atom in a general pure state and the field in avacuum state, we show that the final density matrix is supportedon \({\mathbb C}^2\otimes{\mathbb C}^2\) space, and therefore, theconcurrence can be used as a measure of entanglement between theatom and the field. The influences of the cavity decay on thequantum entanglement of the system are also discussed. We alsoexamine the Bell-CHSH violation between the atom and the field andshow that there are entangled states for which the Bell-BCSHinequality is not violated. Using the above system as a quantumchannel, we also investigate the quantum teleportation of ageneric qubit state and also a two-qubit entangled state, and showthat in both cases the atom-field entangled state can be useful toteleport an unknown state with fidelity better than any classicalchannel.     

Tunable dual-wavelength operation of an external cavity semiconductor laser

Tunable dual-wavelength operation of a laser diode has been achieved using a dual-period holographic element. The holographic element was positioned in Littrow configuration in an external cavity. The design of this holographic element was based on the superposition of a constant-period grating and a variable-period grating on the same location in a photoresist. We observed simultaneous emission at two wavelengths from a visible semiconductor laser operated with this holographic element. The spectral separation of the dual-wavelength output was varied from 0.76 to 6.27 nm by a simple translation of the holographic element.     

Extended temperature tuning of an external cavity diode laser

We describe the construction and operation of an external cavity diode laser in which the diode is cooled to -45 °C. This technique allows us to pull the wavelength of a nominally 782 nm diode to operate at 766.7 nm, a change of over 15 nm. The important aspects of our design are its ease and low cost as compared to other designs of changing the operating wavelength of laser diodes. We provide background information on thermal design with multiple TECs so the reader can extend this example for use in their own applications. PACS 42.60.By; 42.62.Fi; 32.80.Pj     

Sub-Doppler spectroscopy with an external cavity quantum cascade laser

The linewidth of an external cavity quantum cascade laser is studied as a function of injection current and laser scan rate. The laser linewidth is inferred to be ca. 2.5 MHz from Lamb-dip spectra on a low pressure sample of NO and its variation with injection current is well modeled using literature values for the intrinsic material properties of the lasing medium. The laser linewidth measurements are corroborated by polarization spectroscopy studies as well as by analysis of hyperfine structure and cross-over resonances.     

Different kinds of bistable behaviour of a GaAlAs diode coupled to an external cavity of variable length

Experiments and theory on optical feedback effects for different delay times in a system consisting of a GaAlAs-DH diode coupled to an external resonator are presented. Two hysteresis types are found, for short and long delay times. In the case of short optical delay the low-power hysteresis branch corresponds to the noise level below the lasing threshold, whereas for a long delay regular or irregular pulsations of considerable mean power occur. On the upper power level c.w. single-mode emission is dominant for both of the hysteresis types. Dynamic losses due to spectral bandwidth changes may explain the different behaviour.     

Bistable operation of a tunable laser with and without absorber coupled to an external resonator

The stationary states of a single-mode laser with feedback from a grating of high selectivity are investigated theoretically. The amplifying and absorbing media are contained in a Fabry-Perot cavity (FP) of lengthl. The grating and one of the FP end mirrors facing it are forming an external resonator (ER) of lengthL whereLl. The losses in the compound system consisting of the FP and ER depend on the refractive indices of both the media which change with light intensity. An inequality has been derived yielding conditions for unstable operation at lasing threshold connected with a transition of light intensity to the upper branch of a hysteresis cycle. It has been found that a hysteresis in a system without an absorber can arise by tuning the grating frequency towards a FP resonance from the high-frequency side provided that this resonance stands on the high-frequency side of the atomic transition. For the reversed tuning situation the FP resonance must be located on the low-frequency side of the atomic transition. If an absorber is present hysteresis cycles at both sides of a FP resonance can occur independently of its position with respect to the atomic resonances.     

Active wavelength control of an external cavity quantum cascade laser

We present an active wavelength control system for grating-based external cavity lasers that increases the accuracy of predicting the lasing wavelength based on the grating equation and significantly improves scan-to-scan wavelength/frequency repeatability. The ultimate 3?? precision of a frequency scan is determined by the scan-to-scan repeatability of 0.042?cm^?1. Since this control method can be applied to any external cavity laser with little to no modification, such a precision provides an excellent opportunity for spectroscopic applications that target molecular absorption lines at standard atmospheric conditions.     

Extension of the mode-hop-free tuning range of an external cavity diode laser based on a model of the mode-hop dynamics

We report on a universal method to achieve and sustain a large mode-hop-free tuning range of an external cavity diode laser based on a model of its mode-structure dynamics. Using this method, we were able to scan 73 GHz mode-hop free by using an uncoated off-the-shelf laser diode with a central wavelength of 785 nm. Our model applies to any laser system requiring synchronization of more than one optical element.     

Wavelength tuning characteristics of a fabry-perot semiconductor laser with an external short cavity

Wavelength tuning characteristics of a Fabry-Perot semiconductor laser with an external short cavity are analyzed, in which the oscillation wavelength can be changed by slightly altering the external cavity length. Analysis is based on rate equations for an optical power and carrier density. It is shown that the wavelength tuning range is dominated by a change of carrier density through the effect of carrier-induced refractive index change in the active layer of a laser diode. This depends on effective coupling coefficients of the optical field iteratively reflected back to the laser diode by the external mirror, and on reflection coefficients of an anti-reflection coated laser facet and the external mirror which compose the external cavity. The effective coupling coefficient is also derived using the waveguide theory and Kirchhoff ’s theory. Finally, an unstable condition which may limit a stable wavelength tuning range is shown by results of a linear stability analysis of rate equations.     

Spectral beam combining of a broad-stripe diode laser array in an external cavity

The outputs from an 11-element, linear diode laser array with broad stripes have been beam combined into a single beam with a beam quality of ~20x diffraction limited in the plane of the junction. This beam combining was achieved by use of a common external cavity containing a grating, which simultaneously forces each array element to operate at a different, but controlled, wavelength and forces the beams from all the elements to overlap and propagate in the same direction. The power in the combined beam was 50% of the output from the bare laser array.     

Bistable operation of a GaAs-AlGaAs diode laser coupled to an external resonator of narrow spectral bandwidth

The influence of an external dispersive resonator on the emission properties of a double heterostructure semiconductor laser operating at room temperature has been investigated. The proper design of the external resonator (frequency selectivity and efficient back-coupling of the radiation leaving the diode) demonstrates that a laser with optical feedback can show bistability and hysteresis phenomena. The dispersive bistability has its origin in the dependence of the refractive index on carrier density, temperature and optical power. Hysteresis curves have been measured by changing the injection current or by tuning the dispersive element. We have found a threshold in the injection current for the onset of the hysteretic behaviour. Moreover, a theoretical model has been established to explain the essential features of the experimental results. Hysteresis cycles for different experiments have been calculated.