Tunable transform-limited pulse generation using self-injectionlocking of an FP laser

Wavelength-tunable, near transform-limited pulses have been generated using a Fabry-Perot laser diode coupled to a fiber loop containing a fiber Fabry-Perot resonator (FFPR) and a polarization controller. The ratio of transmitted to reflected light from the loop can be adjusted using the polarization controller. Single-mode operation of the gain-switched laser is achieved by self-injection locking, which is induced by light reflected from the fiber loop. The resulting output pulse has a time-bandwidth product of 0.4 and is tunable over about 15 nm by varying the tuning voltage of the FFPR     

Dynamic behavior of reflection optical bistability in a nonlinearfiber ring resonator

We present an analysis of the dynamic behavior of a nonlinear fiber ring resonator when an optical pulse with an arbitrary shape envelope is incident into it through a fiber directional coupler. The transient analysis is based on the extension of a well-known multiple-beam interference method to non-linear transmission problems. The steady-state analyses reported so far predict that the ring resonator exhibits reflection optical bistability in the input-output characteristics under appropriate conditions. But, our transient analysis shows that a nearly periodical oscillation of the transmitted power always takes place at a suitable initial detuning when the resonator has no loss or a small loss. It seems that the present instability is caused by the repetition of accumulation and release of the power in the ring resonator. We can obtain a bistable hysteresis loop by introducing a loss to the directional coupler. The dynamic behavior of bistability in a nonlinear fiber ring resonator with coupler loss is then investigated. It is found that a remarkable undershoot and overshoot occur in the switch-off curve and switch-on curve, respectively     

A novel fiber-optic Fabry-Perot resonator with two mode-conversionmirrors: proposal and application

A novel fiber-optic Fabry-Perot resonator composed of a piece of fiber with two LP₀₁&rlarr2;LP₀₂ mode-conversion reflectors is proposed and theoretically investigated. The reflective fiber-optic LP₀₁&rlarr2;LP₀₂ mode converter is analyzed based on the coupled-mode theory. The resonance characteristics including the transmission, reflection, and circulation of this novel fiber resonator are examined. In addition, we also describe the application of this device as an optical filter which can be used for FDM/WDM communications, etc. In contrast to a conventional Fabry-Perot optical filter with a periodic output spectrum, our proposed optical filter has only one peak in output spectrum, while the bandwidth of the filter spectrum is very narrow, with several Megahertz determined mainly by the cavity length of the fiber resonator. Finally, it is demonstrated that the characteristic of this optical frequency filter can be greatly improved by introducing a gain mechanism using a rare-earth-doped fiber. The tunable performances of this optical filter are also presented     

Fiber-coupled short Fabry-Perot resonators

An air-gap Fabry-Perot resonator with plane mirrors between closely spaced fiber ends may yield low throughput because of the poor match between the modes of typical single-mode fibers and the resonant mode in the air-gap cavity. The throughput can be improved by confining the resonant mode by a hollow dielectric tube placed inside the resonator. Short fiber-coupled Fabry-Perot resonators with and without an inserted hollow dielectric waveguide and expressions for their transmission losses are derived. It is shown that the throughput of both types of resonator can be improved significantly by using fiber with large mode size to couple to the resonator. The special fiber is then spliced to a conventional single-mode fiber. It is concluded that the resonator with an inserted hollow dielectric waveguide offers increased throughput for resonators with high finesse     

Two different mode interactions in an electron tube with a Fabry—Perot resonator—The Ledatron

An electron tube with a Fabry-Perot resonator for the generation of millimeter and submillimeter waves, the Ledatron, has been investigated both theoretically and experimentally. Two different mode interactions, Fabry-Perot mode and surface wave mode, were predicted and found to exist. These two modes can be separated by proper selection of the mirror spacing of the Fabry-Perot resonator in the tube. These two mode oscillations have different characteristics. In the case of the Fabry-Perot mode, the oscillating frequency is tuned mainly by variation of the mirror spacing, that is, mechanical tuning is predominant. On the other hand, in the case of the surface wave mode, electronic tuning predominates. For gratings of the same physical size, the surface wave mode oscillator needs a larger electron accelerating voltage than the Fabry-Perot mode oscillator in order to obtain the same wavelength. The experimental results are in good agreement with our theory of operation.     

High-quality pulse compression in a novel architecture based on a single-mode fiber cascading a nonlinear optical loop mirror

A novel all-fiber low-pedestal pulse compression scheme is proposed and investigated. The scheme is based on an anomalously dispersive single-mode fiber(SMF) cascading a nonlinear optical loop mirror(NOLM) with another anomalously dispersive SMF in the loop. Numerical results show that excellent pulse compression and pedestal reduction can be achieved by using the proposed scheme.     

The transmission and bistability of a nonlinear quasioptical resonator in ESR-conditions in ruby

Due to rapid progress of the nonlinear optics it has become real to observe and use the phenomenon of optics bistability in such passive structure as a Fabry-Perot resonator filled (completely or partially) with a substance having nonlinear adsorbtion and refraction. The problem of the optic bistability of such resonance structures were discussed in [1,2].     

Optical bistability in semiconductor periodic structures

A theoretical demonstration of optical bistability in periodic layered media, particularly in long-period GaAs/AlAs superlattices is presented. The proposed structure consists of a periodic multilayer system, as opposed to previously demonstrated nonlinear bistable devices which employed Fabry-Perot etalons. The optical resonance effect which is essential for bistable devices is, in this case, induced by a refractive index modulation. The nonlinear active medium is distributed in the whole structure rather than placed between the two mirrors of a Fabry-Perot cavity. It is shown by a complete calculation of wave propagation in the periodic nonlinear medium that a multiple valued feature appears in the structure's nonlinear reflectivity spectrum. The input/output characteristics of the structure exhibit bistable hysteresis similar to that of a nonlinear Fabry-Perot etalon     

Coupling efficiency of front surface and multilayer mirrors as fiber-end reflectors

We examine the efficiency with which light is reflected back into a single-mode fiber by front surface and multilayer dielectric mirrors. Coupling losses are due to the penetration of light into a multi-layer dielectric mirror, fiber-mirror separation, mirror tilt, and polishing-induced curvature of the fiber-end face. We also discuss the degradation of the coupling efficiency due to random errors of the optical layer thickness of dielectric mirrors. The results of this paper are needed for the discussion of the performance of a fiber Fabry-Perot interferometer to he presented in a companion paper.     

Spectral characteristics of coupled-waveguide Fabry-Perotresonators and filters

Conventional Fabry-Perot resonators provide a narrow spectral width but lack the capability of longitudinal mode discrimination. A coupled-waveguide Fabry-Perot structure made of two parallel waveguides with reflecting mirrors at the ends is proposed for applications as mode selective resonator in single-mode diode lasers and as narrow-band wavelength filters. The interference of counter propagating waves from reflection by end mirrors and the coupling of waves between the two parallel waveguides contribute to the operation of this resonator structure. Thus, the device exhibits the attributes of both Fabry-Perot resonator and directional coupler. The coupled-mode theory of parallel waveguides is employed to analyze the structure. Both cases of identical and unidentical waveguides are examined. Resonance conditions and spectral characteristics are determined. It is shown that the coupled-waveguide Fabry-Perot resonator provides significant improvement in mode discrimination capability and longitudinal mode spacing over the conventional Fabry-Perot resonator     

External cavity controlled operation of a semiconductor diode gain element in series with an optical fiber

The series combination of a semiconductor diode gain element (a diode laser whose end facets have been antireflection coated) and an optical fiber has been placed inside an external cavity and the combined system has lased in a single spectral line whose width was less than the1.7 times 10^{-5}-nm (7.5-MHz) resolution of the scanning Fabry-Perot interferometer used in the measurement. This result has been achieved with either a single-mode or a multimode optical fiber in series with the diode gain element and for experiments in which a polarizer, oriented so its polarization is parallel to the diode gain element polarization, was placed at the other end of either fiber. The output of the external cavity is temporally stable as measured both by a 225-MHz-bandwidth detector system and a spectrum analyzer. Over a one minute interval the maximum fluctuation in the output frequency of the external cavity was found to be 2 MHz. Analysis of the threshold behavior of the external cavity for the cases where the multimode or single-mode fiber are in the cavity indicates that the coupling coefficients for either fiber are nearly the same. Without an external cavity, the coupling coefficient from the diode gain element (or from a similar, not anti-reflection-coated, laser) to the multimode fiber is over five times larger than that to the single-mode fiber. These coupling results are explained by postulating that for the multimode fiber, only one or a selected number of the many modes of the fiber can participate in the laser action of the external cavity. It is believed that only these mode(s) are reflected back into the fiber by the spherical mirror in appropriate phase and angle to participate in the laser emission.     

Multiple bistability in an optical-fiber double-ring resonatorutilizing the Kerr effect

We present a theoretical study of multiple bistability in an optical-fiber double-ring resonator. The multiple bistability is caused by the optical Kerr effect, which modulates the refractive index of the fiber. The dependence of the multiple bistability on various parameters of the fibers and the couplers is investigated     

A novel integrated micromachined tunable laser using polysilicon3-D mirror

A prototype tunable laser of ~2 mm×1.5 mm size has been developed for wavelength-division-multiplexing (WDM) application. This device is an integrated micromachined polysilicon three-dimensional (3-D) mirror with a single-mode Fabry-Perot laser diode and an antireflection-coated optical fiber. The micromirror can be driven to move laterally by an electrostatic comb-drive that changes the external cavity length of laser diode enabling wavelength tuning. A wavelength-tunable range of 16 nm is obtained using a driving voltage within ±3 V at a bias voltage of 10 V     

Analysis of optical bistability in a nonlinear distributivelycoupled resonator

A nonlinear distributively coupled resonator (NDCR) used as a bistable element is studied. The resonator is an integrated optics implementation of a nonlinear Fabry-Perot resonator with a variable reflectivity mirror. Under certain conditions, the intensity-dependent reflectivity and tuning of the resonator contribute constructively and enhance nonlinear properties of the device. Numerical methods are used to optimize NDCR design parameters and show that the critical intensity required for onset of bistability is reduced by 30% relative to a comparable regular Fabry-Perot. Similarly, the minimum required index change is reduced by 10%     

Measurements and modeling of reflective bistability in 1.55-μmlaser diode amplifiers

We present experimental measurements of bistable characteristics for the case of a 1.55-μm symmetric Fabry-Perot laser amplifier with a particularly rich variety of behavior for reflected signals. Three main forms of hysteresis loops are observed on reflection. The hysteresis loop changes from anticlockwise to clockwise hysteresis in the optical output-input characteristic when the drive current or initial phase detuning is changed. A “butterfly” hysteresis loop is observed experimentally at an optical input power as low as 300 μW for a drive current equal to 94% of the lasing threshold. The dependence of the reflective optical bistability on drive current, initial phase detuning, and injected optical pewter has been investigated for the first time in an uncoated 1.55-μm amplifier. Measurements of the device voltage shifts on switching reveal hysteresis loops which match those in the corresponding optical powers and which indicate the amount of gain saturation and nonlinear refraction responsible for bistability. An analytical model is used to describe the observed reflective bistability and to give insight into the detailed physical mechanisms responsible     

Mean field theory of optical bistability in a phase-conjugate resonator using nearly degenerate four-wave mixing

A mean field theory of nearly-degenerate four-wave mixing is developed for the optical bistability, which has recently been found in a phase-conjugate resonator consisting of a normal mirror and a phase-conjugate mirror under relatively strong pumping. The bistability in transmission of the probe beam occurs as the mirror separation or the probe offset frequency is changed, but for a limited range of probe beam intensity. This behavior is explained as occurring under injection-locked conditions because of combined effects of tilting and broadening, or narrowing of the resonance curves due to nonlinearities in the phase-conjugate reflectivity arising from pump depletion.     

Characteristics of millimeter wave detection in a Fabry-Perot resonator using a YBCO-BiO composite superconductor

A quasioptical technique with a hemispherical-type Fabry-Perot resonator for measuring characteristics of millimeter wave detection using a YBCO-BiO composite superconductor has been successfully developed. This Fabry-Perot resonator consists of a spherical mirror and a plane mirror mounted on the cold head of the refrigerator, under a controlled temperature of 40 to 300 K. The method offers the advantages of estimating irradiation power, easily controlling the sample temperature, analyzing the mode of the irradiated millimeter waves and easily extending to higher frequencies. The superconducting millimeter wave detector has been measured with this technique, with measured sensitivities of 46.5 V/W (70 K) to 160 V/W (35 K) at 50 GHz. These results are close to the theoretical values calculated numerically from the characteristics of the detector. It was confirmed that the millimeter wave detection system using the Fabry-Perot resonator is suitable for estimating the sensitivity of the high-Tc superconducting millimeter wave detector.     

NOLM-NALM fiber ring laser

We study the bidirectional lightwave propagations in an erbium-doped fiber ring laser and an inverted-S fiber ring laser, and observe their optical bistability behaviors. We develop a model for the inverted-S fiber ring laser using nonlinear optical loop mirror and nonlinear amplifying loop mirror (NOLM-NALM) principle, which operates in the nonlinear region. Good agreements between the laser experimental performance and the developed model are achieved. The laser shows good switching and pulse compression capabilities. In addition, the laser model illustrates the route to chaotic operation via period doubling bifurcation, when the input power increases. We also obtain quasi-periodic operation when the laser is amplitude modulated experimentally.     

光通信系统中新型可调谐半导体激光器的设计

为了适应当前光通信系统对波长可调谐激光器的需求,提出用游标效应来实现波长可调谐的激光器,设计了一种功率稳定且频率可调的三段式开槽法布里-珀罗结构可调谐半导体激光器,给出了系统结构的设计原理,并进行了理论分析和实验验证。取得了三段式开槽法布里-珀罗结构可调谐半导体激光器激射谱叠加图数据,利用光纤延迟自外差法测量激光器线宽,对比了3种不同激光器的线宽测量曲线。结果表明,基于游标效应设计的新型开槽法布里-珀罗可调谐半导体激光器波长调谐机制简单方便,且具有很好的单模性和信道切换能力。该研究在未来的光通信领域中具有一定的应用价值和实际意义。     

Refractive Fabry-Perot bistability with linear absorption: Theory of operation and cavity optimization

We present a theory of optical bistability for a Fabry-Perot cavity containing a medium with nonlinear refraction but linear absorption with only plane-wave and slowly varying envelope approximations. An analytic expression for the critical intensity Icfor the onset of bistability is derived and used to compare cavity designs. It is shown that 1) the important material parameter for minimum Icis the ration_{2}/alpha 2) the limit to Icis set by limitations on finesse due to inhomogeneities rather than the absorption itself, and 3) the cavity design which gives lowest Icfor a given finesse is that for which the mirror transmissivity equals the absorption per pass; at high finesse this design leads to a total peak cavity transmission of 1/4 when mirror reflectivities are equal.