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To obtain pulsed light signal used as pulsed pump light for optical fiber sensing and communication systems, a design scheme of generating pulsed light based on continuous laser and Field Programmable Gate Array (FPGA) is proposed in this paper. The pulsed light signals with minimum pulse width of 10 ns were obtained in the experiment, the pulse widths of the pulsed light signals could be regulated with the smallest increment of 5 ns, while the deviations of the pulse widths were less than 0.8 ns between the measurements and the expected values. The repetition frequency could also be adjusted from 0.05 Hz to 100 MHz. Not only is the pulsed light signal stable and reliable, but the complexity of the system is also reduced by using the design method in this paper.

This paper presents a theoretical investigation of the effects of the induced uniaxial anisotropy on the excitation and propagation of magnetostatic volume waves under the inclined bias magnetic field. The cases of both the easy axis normal and parallel to the film have been considered. The numerical results for bismuth-doped yttrium-iron-garnet film show that the induced uniaxial anisotropy has significant effects on excitation and propagation characteristics of magnetostatic volume waves. In particular, the induced uniaxial perpendicular anisotropy contributes to improving the delay linearity, enhancing the excitation efficiency, increasing excitation bandwidth and lowering the insertion loss for magnetostatic volume waves under appropriately inclined magnetic field. Thus, significant improvements in device performance can be realized by using the magnetic film that possesses appropriate induced uniaxial anisotropy.

This paper presents a theoretical investigation of the effects of the induced uniaxial magnetic anisotropy on Bragg diffraction and mode conversion of a guided optical wave (GOW) by a magnetostatic backward volume wave (MSBVW). The cases of both the easy axis normal and parallel to the film have been considered. The numerical results for a Bi-doped yttrium–iron–garnet–gadolinium–gallium–garnet (YIG–GGG) waveguide show that the induced uniaxial anisotropy has significant effects on the mode conversion efficiency of GOW and magneto-optic coupling bandwidth. In particular, the induced uniaxial perpendicular anisotropy can enhance the mode conversion efficiency and magneto-optical bandwidth. Thus, the performances of MSBVW-based magneto-optical waveguides can be improved by using a magnetic film that possesses the induced uniaxial perpendicular anisotropy.

The power characteristics for magnetostatic waves (MSWs) propagating in a double-layered YIG waveguided structure are theoretically studied under inclined magnetic field. The transmission power spectra of MSWs have been obtained at the different inclination angles of the field θ⩽20°. The results indicate that the power is strongly dependent on the inclination angle of magnetic field, particularly, in the high-frequency range. The propagation characteristics of MSWs in the double-layered magnetic waveguided structure are superior to that in the single layer. The former can effectively enhance the transmission power of MSWs, and it will benefit the MSW technology to apply to the broadband transmission area of signal processing and communication. In addition, the study indicates that the lower magnetic layer with the appropriate magnetization in the double-layered waveguided structure can also increase the transmission power of MSWs. It can be achieved to adjust propagation characteristics and to improve propagation quality more effectively by the way of alternating the kinds of the double-layered magnetic films.

The noncollinear interaction between the guided optical waves (GOWs) and magnetostatic forward volume waves (MSFVWs) is theoretically studied in a double-layered waveguide under inclined magnetic field. The diffraction efficiency (DE) and the mode-conversion efficiency of GOWs are calculated numerically at the different inclination angles of the field. The results indicate that the double-layered waveguide, in which the top magnetic layer is made of the Bi-doped YIG film, can enhance the DE of GOWs. Under the phase-matching conditions, the DE may be greatly enhanced by using an appropriately inclined magnetic field in the double-layered waveguide. In addition, by varying the inclination angle of the field and the interval of the double-layered waveguide, the magneto-optical (MO) coupling between the GOWs and MSFVWs can be adjusted in the larger range. It is possible to improve the performances of the MO waveguide devices more effectively.

The noncollinear interaction of guided optical waves with magnetostatic waves under inclined bias magnetic field is theoretically studied in detail. Similar approach can also be applied to the collinear interaction. Calculation results indicate that the diffraction efficiency (DE) in magnitude is equal to the mode-conversion efficiency (MCE) under vertical bias magnetic field, but they differ greatly under inclined bias magnetic field. By comparison to the case of vertical magnetization, the DE or the MCE can be greatly increased under inclined magnetic field. The characteristic of the DE curves obtained is basically in agreement with the experimental result.

Under inclined magnetic field, the propagation characteristics of magnetostatic waves (MSWs) for a double-layered waveguided structure are theoretically studied by using surface permeability method. A new concept called ‘mode interlamination coupling’ is proposed by analysis of mode spectrum, which develops a generalized understanding of the MSWs propagating in a layered structure. A similar treatment can be applied to the situation of multi-layered structure under inclined field. In addition, the dispersion relation and delay characteristics of coupled mode in two different YIG films are studied by numerical analogue at inclination angle from 5 to 20°. The results indicate that the MSWs propagating in double-layer structure is appropriate for high frequency range (8.4∼10 GHz) under inclined field, and it has an optimum range of delay rate superior to single film by adjusting the inclination angle of the magnetic field. Apparently, the performances of double-layered film structure under inclined field have potential dominance in channelization and stability of signal processing for the application of magneto-optic waveguided devices in the future.

The noncollinear interaction between guided optical waves and magnetostatic waves under inclined bias magnetic field is studied in detail. The diffraction efficiency (DE) and the mode-conversion efficiency (MCE) of guided optical waves with magnetostatic forward volume waves in the bismuth-doped yttrium–iron–garnet (Bi-doped YIG) waveguide are calculated numerically. The calculation results indicate that the DE and the MCE are different in physical conception and the DE is not equal to the MCE in magnitude under inclined bias magnetic field. The DE may be greatly increased by using an appropriately inclined bias magnetic field, which has been experimentally confirmed in a pure YIG waveguide. By using an inclined bias magnetic field and the Bi-doped YIG waveguide, under the phase-matching conditions, the maximum DE can come up to 79.5% or more.

It is found that, in contrast to the usual situation of a uniform bias magnetic field perpendicular to the YIG-film plane, a tilted bias magnetic field results in modification to the phase matching condition, and may possibly facilitate enhanced MO Bragg diffraction efficiency. On the other hand, recent experiments also show that the Bragg diffraction efficiency could be significantly enhanced by utilizing a bias magnetic field which is nonuniform but still perpendicular to the waveguide film plane. A diffraction efficiency as high as approximate 70% has been measured in comparison to a 12% diffraction efficiency for a typical modulator utilizing a uniform magnetic field. In this paper, a summary of theoretical treatment for Bragg diffraction under tilted bias magnetic field and some of the most recent experimental results for Bragg diffraction under nonuniform bias magnetic preliminary result presented.

Coupled-mode equations for Stokes and anti-Stokes interactions of guided optical waves with magnetostatic forward volume waves under inclined magnetic field are given. Calculation results indicate that, only at normal magnetization, the diffraction efficiency (DE) is equal to the mode-conversion efficiency (MCE) in magnitude; by comparison to the case of normal magnetization, the DE and the MCE can be increased greatly under appropriate inclined magnetic field. For the YIG waveguide used, the DE for the Stokes interaction is much greater than that for the anti-Stokes interaction when the inclined angle|θ| < 25° and the MCE is symmetrical about θ. For the Bi-doped YIG film, the MCE presents a rapid oscillation with θ. The obtained results tally with the experiments.

The characteristics of magnetostatic forward volume waves (MSFVWs) propagating in magneto-optical (MO) film waveguide under inclined bias magnetic field are analyaed. The dependences of MSFVW propagation constant and dynamic magnetization related to the MO coupling coefficients on mode number, frequency and inclined bias magnetic field are calculated in detail. It is shown that the greater the MSFVW frequency f and the mode number m as well as the less bias magnetic field Hi and inclination θ, the greater MSFVW propagation constant Ks is; the amplitude of zero-mode MSFVWs is much greater than that of high-mode MSFVWs. In an appropriate frequency range, MSFVW amplitude can be increased under an inclined bias magnetic field, and then the diffraction efficiency of guided optical waves with MSFVWs is improved.

A theoretical Treatment is presented on the propagation characteristics of magnetostatic forward volume waves and related guided-wave magnetooptic (MO) Bragg diffraction in an YIG-GGG waveguide under an inclined bias magnetic field.It is found that,in contrast to the usual situation of a perpendicular bias magnetic field,an inclined bias magnetic field leads to the modification to the phase matching condition and,as a result of increased Faraday effect etc.,facilitates enhancement of MO Bragg diffraction efficiency.Such an efficiency enhancement enables utilization of low-propagation loss materials such as the pure YIG for construction of viable guided-wave MO Bragg devices.The theoretical predictions are in good agreement with the experimental results.

There is evidently a difference between the dynamic and static Faraday effects in magnetooptical medium.The real part θ′t of the alternating Faraday rotation θt all is less than the real part θ′s of the static Faraday rotation θs,and the imaginary part θ″t all is bigger than the imaginary part θ″s.It is shown by the experimental result of Faraday effect in (BiTm)3(FeGa)5O12 films that the frequency dependence of θt has a direct bearing on the mechanism of magnetic lag in the high-frequency region of ω>104Hz,and is mainly depend on the magnetic hysteresis in the low-frequency region of ω≤103Hz.Even if ω→0,θt does not equal θs as a result of the magnetic hysteresis loss in the medium.It is also indicated by the theoretical analysis that it is impossible to realize completely the on off state of the switch for a modulator utilizing the magnetooptical medium with magnetic losses.

A magnetostatic delay line (MSDL) composed of a longitudinally magnetized YIG single crystal rod is constructed. The multiple round trip echoes observed, especially at short delay times, are sucessfully suppressed by changing the sample shape. At S-band the useful delay time controlled magnetically ranges from 0 to 0.5 μs. The untuned insertion losses at 2 and 4 GHz are ⩽26 dB.