To obtain higher pulse energy and pulse peak power of Q-switched fiber lasers, the length of amplifying fiber should be
optimized properly. In this paper, the optimum length of fiber for maximum pulse energy or maximum pulse peak power
is investigated based on the rate equations of Q-switched fiber lasers. The relationship between the optimum fiber length
and the output coupler reflectivity is got by using the mathematical technique of Lagrange multipliers and numerical
analysis. As a result, output pulse energy and pulse peak power can be expressed as functions of the fiber length,
multiplied by a few simple constants. The results show that, at given pump power level and round-trip parasitic loss,
there is a demarcation of output coupler reflectivity which is inversely proportional to the round-trip parasitic loss
coefficient. Fiber length should be optimized to achieve maximum pulse energy when the output coupler reflectivity is
less than the demarcative reflectivity, and on the contrary, it should be optimized to yield maximum pulse peak power.
A novel all-optical high speed sampling method using nonlinear polarization rotation (NPR) in a semiconductor optical amplifier (SOA) is proposed in this paper. Using the carrier rate equation in a SOA for the propagation of an optical pulse, a model is proposed to describe the relationship between the polarization rotating angles of probe light and the pump light power. Meantime, affection introduced by the initial polarization of the probe light, as well as the injected current of the SOA is studied. The numerical results indicated that the initial polarization of the probe light affects the transfer curve between the output light power of probe light and the pump light power, and the injected current of SOA could affect the linearly dynamic range and the rise slope of the transfer curve. In order to obtain suitable slope and larger linear dynamic range, the parameters are optimized. The primarily simulated results indicated that the pump light power is not more than 1mW. It is also shown that the all-optical sampling mentioned in this paper has promoting potential to improve the sampling rate at hundreds GS/s and needs considerable lower optical power than others.
Single mode propagation is an important requirement for optical waveguide devices for use with single-mode fiber, it
can reduce the coupling loss. In this paper, a technique is used for calculating the field distribution of the polymeric
Y-junction rib waveguide. The technique is based on the combination of the effective index method(EIM) and the
variational method(VM). It is mixed between the advantages of each method and avoided their disadvantages, where EIM
can make the calculations procedures simple but it has some difficult to find the field distribution, other wise, VM can be
used with very good accuracy to find the field distribution. An algorithm is implemented to study the effect of the
structure parameters on the field distribution of the polymeric Y-junction rib waveguide. In our simulation, the core layer
is PU-FTC (email@example.comμm),the cladding layers were NOA73 (firstname.lastname@example.orgμm) and Epoxylite9653 (email@example.comμm).
The obtained single mode rid waveguide structure parameters are: the core thickness is 1.5μm, the rib height is 0.2μm,
the rib width is 5μm.