SOLUTION BRIEF
How to Prevent Feedback and Damage in Ultrafast Fiber 온라인카지노s using Coherent Optical Isolators
1 The Effect of Feedback on Femtosecond Fiber 온라인카지노 Systems
A little (온라인카지노) feedback can go a long way . . .
Rare-earth doped optical fiber has become a more widespread medium for ultrafast 온라인카지노 systems in both fiber-only and hybrid (fiber and bulk) 온라인카지노s. However, there are design issues inherent to fiber-based oscillators and amplifiers. Because fiber is a high gain medium, any light that is inadvertently injected into the ultrafast oscillator, as well as into amplifiers, can degrade and potentially irreversibly affect system performance by causing instability (at best) or damage (at worst). Optical feedback is caused by back-reflections off of downstream optics or by amplified spontaneous emission (ASE) from amplifier stages, and it is amplified by the high gain in doped optical fibers. Small signal, single-pass gains of ~ 20 dB or more are typical in optical fibers, as opposed to the relatively lower gain of ~ 5 dB in bulk doped materials. The relatively smaller size of the beam at the end of a fiber, compared to bulk gain material, leads to higher intensity at the end face, and creates scenarios where fiber systems can reach the damage threshold at lower optical powers.
Glass fiber host 온라인카지노 media are “high gain”
- Geometry 온라인카지노lows for more gain in a single pass than in bulk systems
- Gain can be up to 100x or more
- For Oscillators, output coupler can be ~ 70% or more
Generating pulses below 10 picoseconds (ps) and into the femtosecond (fs) range, ultrafast 온라인카지노 systems can be designed for a range of operating regimes, depending upon target pulse energies and repetition rates. Two typical configurations are 1) an optical Master Oscillator Power Amplifier (MOPA) scheme for ps pulses and often with hybrid bulk-fiber design, and 2) a Chirped Pulse Amplifier (CPA) scheme for fs pulses. Examples of these designs can be seen in Figures 1 and 2.
Practically speaking, whenever a 온라인카지노 system is designed using a mode-locked fiber oscillator as the pulse source, the oscillator typically provides only mW level output while system requirements can go to the 10s of Watts and beyond. Amplifiers are required to achieve performance targets, and often use large-mode area (LMA) amplifiers producing 1W to even up to more than 100W. But the oscillator can only remain stable with feedback on the microwatt (μW) level or less. Otherwise, noise that disturbs the spectral content can inhibit mode-locking or even cause Q-switching– the power that is fed back must be smaller than the ASE that pulses build from; this often means that an oscillator requires << 60 dB of feedback to remain stably mode-locked. In contrast, solid-state mode-locked oscillators can still operate with many times that amount of feedback. At the same time, if the seed pulse from the oscillator is interrupted at the input of an amplifier, Q-switching can result, which invariably leads to optical damage on a fiber end face.
A mechanism to prevent feedback from entering ultrafast 온라인카지노 oscillators, and to protect the subsequent chain of amplifiers, is essential.
Fortunately, there is a solution to the problems arising from 온라인카지노 feedback the use of Coherent 온라인카지노 Isolators.
2 Using a Faraday Isolator to Protect against 온라인카지노
A Faraday Isolator is an optical device that provides high transmission of signal light in the forward direction, but strongly blocks light from the reverse direction. The main component in an optical isolator is the Faraday Rotator, which is made of a magneto-optic material with special properties; the Faraday Rotator operates by rotating the plane of polarized light 45 degrees in the forward direction and an additional 45 degrees of non-reciprocal rotation in the reverse direction, while maintaining the light’s linear polarization. When placed between crossed polarizers, a Faraday Rotator becomes a Faraday isolator. A Faraday Isolator protects 온라인카지노 oscillators and 온라인카지노 amplifiers from the deleterious effects of back reflections. Containing low absorption, high damage threshold optics, our Faraday Rotators and Isolators are ideally suited for use with average power levels of up to 50W for ultrafast 온라인카지노 systems.
When selecting an isolator, there are several criteria to keep in mind: the incident beam size, the incident 온라인카지노 power on the isolator, the required transmitted power for the next stage, and the amount of isolation required.
Find theCoherent Faraday 온라인카지노that’s best suited for your requirements or now.
Figure 1:Typical MOPA Design, showing the use of 온라인카지노s (denoted ISO) and their locations in the beam path.
Figure 2:Typical CPA Design, showing the use of 온라인카지노s (denoted ISO) and their locations in the beam path.
3 Installing a Faraday 온라인카지노
Installing a Faraday Isolator in the optical path of a fiber 온라인카지노 system is relatively straight forward. Each Coherent Isolator comes with a User’s Manuali, which describes how to align the device in the beam path. The parameters of 온라인카지노 beam size, 온라인카지노 power and center wavelength and bandwidth must be taken into account when selecting the appropriate isolator as each are made to the exacting specifications of the selected model.
See Figures 1 and 2 for examples of where to install 온라인카지노s in MOPA and CPA systems. An example of a real-world application can be found in reference 2ii.
4 Considerations Related to Dispersion
Dispersion is a significant issue for ultrafast 온라인카지노s, one that can affect the pulse duration and therefore, the peak power, of ultrashort pulses. Dispersion occurs when light pulses travel in a medium where the phase velocity depends on its frequency (or wavelength). The Faraday material used to make an optical isolator is dispersive, and therefore pulses traversing through an isolator can broaden in length, although the magnitude and relevance of that effect depends on both the initial pulse and the application.
Generally, fiber 온라인카지노 systems produce pulses on the order of 100 fs or longer, with an optical bandwidth in the range of 10 - 30 nm or more. The actual system bandwidth, along with the length of the Faraday Rotator used in the isolator, will dictate the amount of pulse broadening that will occur. The amount of dispersion typically will not cause enough pulse distortion to negatively impact applications.
However, it is important to note that for pulses < 100 fs (pulses with broader bandwidth), the amount of dispersion will be greater - and this becomes an important consideration in many applications. As an example, in nonlinearly broadened systems, including certain CPA systems, it is possible to produce < 100 fs pulses. If an isolator is required at the output of the 온라인카지노 system due to the possibility of feedback from the 온라인카지노 application, such as in material processing, this will add to the overall group velocity dispersion budget. In some cases, the effects of dispersion caused by the output isolator can be mitigated or removed by balancing it with dispersion in other parts of the system.
An example of how a Faraday 온라인카지노 using 8 mm of TGG can affect the pulse duration of ~ 1050 nm ultrashort pulses over the range from 10 – 10,000 fs, is shown in Figure 3. The graph was generated by determining how much group velocity dispersion (GVD) occurs for 1050 nm pulses. This was done using the Sellmeier Equation for TGGiii.
The group velocity dispersion (GVD), which introduces a frequency dependent delay to the different spectr온라인카지노 components of the pulse (typic온라인카지노ly in units of fs2/m) is expressed asiv:
Solving an온라인카지노ytic온라인카지노ly for the 2ndderivative of the refractive index, it is possible to c온라인카지노culate GVD and then the actu온라인카지노 second order dispersion for a specific device (here denoted as β2, the second-order group delay dispersion), related to GVD by multiplying GVD by the length of the material – in this case, the TGG used in the 온라인카지노. This information can in turn be used to calculate the output pulse duration for given input pulse duration, after traveling through the length of TGG 온라인카지노 material. For the case where the input pulse length squared, t0 2 , is much less than β2, an equation to express the pulse broadening proportion온라인카지노 to β2can be usedv.
By performing these c온라인카지노culations, the amount of dispersion, β2, over the range of 1030 - 1080 nm was found to be ~ 1100 fs2for 8 mm long TGG. The estimated broadening from that amount of second order dispersion for pulses in the range of 10 – 10,000 fs is shown in the graph below.
Figure 3:Broadening of a femtosecond pulse at ~ 1050 nm after propagation through 8 mm of TGG (blue curve); the red curve shows the output for undistorted pulses.
5 Conclusions
When designing ultrafast 온라인카지노 systems with fiber sub-systems, the use of protective optical isolators is key to achieving the best performance and product lifetime. To maintain stability, robustness, and avoid the deleterious effects of back reflections, the use of Coherent Isolators at critical points in the system will help you achieve the best possible performance and long-term 온라인카지노 system reliability.
Contact us for more information on how to protect your ultrafast fiber 온라인카지노 system from optical feedback.
References:
i Coherent User Manual for Faraday Rotators and 온라인카지노s
ii J. Limpert, T. Schreiber, S. Nolte, H. Zellmer, and A. Tünnermann, "All 온라인카지노 chirped-pulse amplification system based on compression in air-guiding photonic bandgap 온라인카지노," in Advanced Solid-State Photonics (TOPS), G. Quarles, ed., Vol. 94 of OSA
Trends in Optics and Photonics (온라인카지노 Society of America, 2004), paper 9.
iii U. Schlarb and B. Sugg, “Refractive Index of Terbium G온라인카지노lium Garnet”, Phys. Stat. Sol. (b) 182 K91 (1994)
iv As one source, see “Nonlinear 온라인카지노 Optics” by G. P. Agrawal for more details on group velocity dispersion
v See the section on Dispersive Pulse Broadening and Chirping at: