Wavelength tunable, pulsewidth selectable, repetition rate variable, fibre based infra red source

使用被动或主动锁模技术，在传统激光系统中产生短脉冲，其重复率主要由腔的往返时间确定。在绝大多数情况下，腔组件的物理尺寸导致重复率在10兆赫范围内。它通常难以改变，并且如果它是可变的，则通常涉及腔的重新配置。类似地，由锁模技术产生的脉冲的持续时间由腔参数预先确定，并且在大范围内不容易选择。光学滤波器可以放置在腔中以限制带宽，从而影响所生成的脉冲的时间格式。然而，插入这样的滤波器通常需要重新优化腔，并且不能连续地选择脉冲宽度。这就大大限制了传统激光系统的通用性和适用性。我们提出的配置采用单通技术。所产生的脉冲的重复率简单地由在线相位调制器的驱动频率确定。结合发射边沿滤波器，信号被转换成相应的脉冲序列。由于输入信号也是连续工作的激光器，因此可以在种子激光器的整个增益窗口上容易地调谐。为了从该组件获得连续可选择的脉冲宽度，利用了可以使它们在光纤的孤子支持区域中操作的事实。在这里，非线性强度相关的非线性效应可以通过反常色散来平衡。产生的孤子具有固定的“面积”。强度和持续时间的乘积是恒定的，因此，如果孤子可以被放大，并且这必须被自动地进行，使得没有能量从孤子分散，则其持续时间将减小。由光纤中的拉曼增益提供的缓慢的指数增益对于这种缓慢的绝热放大是理想的。增益的控制，简单地允许控制脉冲持续时间，并且通过简单地改变泵浦功率，输出脉冲持续时间在大范围内是连续可选择的。我们建议从窄线铥光纤激光器播种系统，并在一个专门设计的高增益拉曼放大器光纤中放大，在一个全光纤配置中，将允许平均功率高达2瓦，脉冲持续时间可在20皮秒和200飞秒之间选择，重复率在5和10 GHz之间。在短期内，扩展到20 GHz应该是可能的。在光纤非线性光学工艺中使用附加的后续工艺应该允许从1950 nm到2500 nm的连续调谐，在对于医学应用和分子指纹识别重要的区域中提供独特的性能特性。

Using either passive or active mode locking techniques, short pulses are generated in conventional laser systems with a repetition rate that is primarily determined by the round trip time of the cavity. In the vast majority of cases the physical size of the cavity components results in the repetition rate being in the 10s of Megahertz regime. It is often difficult to vary and if it is variable it generally involves a reconfiguration of the cavity. Similarly, the duration of the pulses produced by the mode locking technique are predetermined by the cavity parameters and are not readily selectable over large ranges. Optical filters can be placed in the cavity to restrict the bandwidth and so affect the temporal format of the generated pulses. However, inserting such filters usually requires a reoptimisation of the cavity and pulse widths cannot be continuously selected. This places considerable restriction on the versatility and applicability of conventional laser systems.The configuration we propose employs a single pass technique. The repetition rate of the generated pulses is simply determined by the drive frequency to an in line phase modulator. In conjunction with a transmitting edge filter the signals are turned into a corresponding series of pulses. Since the input signal is also a continuously operating laser it can be easily tuned over the complete gain window of the seed laser. In order to achieve continuously selectable pulse widths from this assembly, use is made of the fact that they can be made operate in the soliton supporting region of an optical fibre. Here the nonlinear intensity dependent non linear effects can be balanced by anomalous dispersion. The generated soliton has a fixed "area". The product of intensity and duration is constant, consequently if the soliton can be amplified, and this must be undertaken adiabatically, such that no energy disperses from the soliton, its duration will decrease. The slow, exponential gain provided by Raman gain in an optical fibre is ideal for this slow adiabatic amplification. Control of the gain, simply allows control of the pulse duration and by simply changing the pump power the output pulse duration is continuously selectable over a large range.We propose to seed the system from a narrow line thulium fibre laser and amplify in a specially designed high gain Raman amplifier fibre in an all fibre configuration that will allow average powers of up to 2 watts, pulse durations selectable between 20 picoseconds and 200 femtoseconds, at repetition rates between 5 and 10 GHz . Extension up to 20 GHz should be possible in the near term. Using additional follow on in fibre non linear optical processes should permit continuous tuning from 1950 nm to 2500 nm, providing unique performance characteristics in a region of importance for medical application and molecular fingerprinting.