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

使用被动或主动模式锁定技术，在传统的激光系统中产生短脉冲，其重复率主要由腔的往返时间决定。在绝大多数情况下，腔体组件的物理尺寸导致重复频率在兆赫的10兆赫。它通常很难改变，如果它是可变的，它通常涉及腔的重新配置。同样，锁模技术产生的脉冲的持续时间是由腔参数预先确定的，并且在大范围内不易选择。光学滤波器可以放置在腔中以限制带宽，从而影响所产生脉冲的时间格式。然而，插入这样的滤波器通常需要重新优化腔体和脉冲宽度不能连续选择。这对传统激光系统的多功能性和适用性造成了相当大的限制。我们提出的配置采用单通道技术。所产生的脉冲的重复率简单地由对在线相位调制器的驱动频率决定。与发射边缘滤波器一起，信号被转换成相应的一系列脉冲。由于输入信号也是一个连续工作的激光器，它可以很容易地在种子激光器的整个增益窗口上进行调谐。为了从该组件中获得连续可选的脉冲宽度，使用它们可以在光纤的孤子支持区域中工作。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。生成的孤子有一个固定的“面积”。强度和持续时间的乘积是恒定的，因此，如果孤立子可以被放大，并且必须绝热地进行，这样就不会有能量从孤立子中发散出来，那么它的持续时间就会减少。光纤中拉曼增益提供的缓慢指数增益是这种缓慢绝热放大的理想选择。控制增益，简单地允许控制脉冲持续时间，并通过简单地改变泵功率，输出脉冲持续时间是在大范围内连续可选的。我们建议用窄线铥光纤激光器作为系统的种子，并在一个专门设计的高增益拉曼放大器光纤中进行放大，在全光纤配置中，平均功率高达2瓦，脉冲持续时间在20皮秒到200飞秒之间可选择，重复频率在5到10 GHz之间。在短期内应该可以扩展到20 GHz。在光纤非线性光学过程中使用额外的跟随线应该允许从1950纳米到2500纳米的连续调谐，在医疗应用和分子指纹识别的重要区域提供独特的性能特征。

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.