Transverse modes of plane-mirror waveguide resonators

The author examines what familiar first-order theory predicts about plane-plane resonator behavior, stressing the similarities and differences between circular-bore and square-bore devices. The effects of moving a mirror away from the guide are discussed, and illustrated with novel results for the modes and losses of single-guide and U-folded designs with square bores. It appears that laser performance cannot be accurately predicted by previous treatments which use only a few (1-3) waveguide nodes     

Coupling losses in hollow waveguide laser resonators

Hollow waveguide gas lasers of the type described by Smith have some inherent loss in coupling radiation from the guide into free space and back into the guide. This paper calculates that loss for the EH11lowest order waveguide mode as a function of mirror position and mirror radius. It is shown that some mirror positions and radii are optimum, in that they provide low coupling loss and are relatively insensitive to mirror position.     

Transverse modes of active hollow waveguide resonators

The effect of an active medium on the mode structure of a hollow waveguide resonator is investigated. A coupled-mode approach is employed. The field propagation through the resonator is described by a propagation matrix; thus, the solution is found by solving the generally nonlinear eigenvalue problem of the matrix for complete resonator round-trip. This has been performed numerically using an appropriate iteration procedure. The method was applied to duel-case I resonators. It was found that thermally induced refractive index profiles and, in the case of larger guide cross sections, the gain properties can also alter the mode structure significantly. These alterations influence the power gain coefficient as well as the conditions for single-transverse-mode operation     

Optical excitation of quartz resonators

Quartz resonators vibrating according to different modes (extensional, flexural, thickness shear, face-shear modes) have been excited with a modulated light beam in the frequency range 1 kHz?1 MHz.     

Dielectric ring resonators loaded in waveguide and on substrate

A rigorous mode matching technique is used to analyze the dielectric ring resonators loaded in a waveguide and on top of a substrate. Variation of several lowest order modes' resonant frequencies as a function of structure parameters is presented and is shown to be helpful for optimization of spurious mode separation. Two-dimensional electric and magnetic field line patterns and three-dimensional field intensity distributions of the ring resonators are plotted and provide information for mode excitation, coupling, and spurious mode suppression. Coupling between two dielectric ring resonators loaded in a metallic cavity are analyzed. The dielectric ring resonators are used to design a C-band elliptic function dual mode bandpass filter employing HE₁₁ modes. Experimental results are presented and show excellent agreement with the analytical solutions     

Canonical ridge waveguide filters in LTCC or metallic resonators

A new physical realization of an elliptic function filter response is proposed for achieving compact size, wide bandwidth, wide spurious free stopband and high-selectivity performance. The filter configuration can be implemented in conventional waveguide technology or embedded in a multilayer low-temperature co-fired ceramic structure for integration with other circuitry in a chip module. The filter is analyzed using rigorous mode matching. To validate the concept, prototypes of four- and six-cavity elliptic filters are designed following a systematic procedure. Approximate synthesis is used to obtain initial dimensions of the filter and the desired optimum response is obtained by means of a final full-wave optimization. The results are verified with other numerical methods and with the measurements of a fourth-order waveguide filter.     

Optical resonators in the approximation of Gauss

A general theory of optical resonators based on the concept of complex point-eikonal is presented. The analysis is limited to the approximation of Gauss. The modes of resonance of open resonators formed by two spherical mirrors facing each other have been obtained in previous works by fitting the wavefronts of Gaussian beams to the mirror surfaces. This method becomes complicated when the resonator contains focusing elements or dielectric slabs. The approach proposed in this paper is more straightforward than previous approaches dealing with this problem and is applicable to resonators containing anisotropic media. The round-trip point-eikonal is first evaluated on the basis of the conventional laws of Gaussian optics. The presence of apertures with Gaussian transmissivity, and of lasers with quadratic transverse variation of the gain, are accounted for by introducing complex round-trip point-eikonals. The modes ψm(x) of the resonator are obtained from a power series expansion of the Green function of a mode-generating system related to the round-trip point-eikonal S of the resonator. The resonance frequencies and the round-trip losses are given by simple and general formulas. The mode fields are described by Hermite-Gauss functions with complex arguments, explicitly in terms of S. For resonators that do not contain apertures, the wavefronts are the same for all the modes and they are plane at planes of symmetry. In reciprocal resonators, clockwise and counter-clockwise modes have the same losses and resonant frequencies, but different mode pattents. These modes are shown to be mutually adjoint. Adjoint modes, with < ψ^†m, ψn> = 0 if m ≠ n, are useful to evaluate the response of optical resonators to incident fields. Results applicable to resonators containing nonorthogonal astigmatic elements are also discussed.     

Optical second-harmonic generation by quasi-phase matching inchannel waveguide structure using organic molecular crystal

Waveguide quasi-phase matching second-harmonic generation (QPM-SHG) using an organic molecular crystal as a nonlinear material was demonstrated for the first time. The device is constructed with an array of SiN channel guides with grooves of a fan-out grating pattern and mNA single crystal grown over the waveguides. A normalized efficiency of 0.04%/W was obtained in an experiment involving frequency doubling of CW Nd:YAG laser light     

Stopband performance improvement of rectangular waveguide filtersusing stepped-impedance resonators

Rectangular waveguide stepped-impedance resonators (SIRs) are analyzed and employed in the design of an X-band filter with center frequency f₀ = 10 GHz and a bandwidth of 100 MHz. An attenuation of 80 dB is held up to 23.1 GHz and, compared to standard uniform-impedance-resonator filters, a reduction in length of 55 % is achieved at the expense of an increased insertion loss from 0.6 to 1.5 dB. The second resonance of the fundamental TE₁₀ mode can be controlled by adjusting the length and impedance ratio of each resonator. A design procedure that takes into account step discontinuities is described and applied to the design of a number of SIR filters. Finally, the presented theory is supported with experimental results     

Theory of waveguide laser resonators with small curvature mirrors

A theoretical investigation into the eigenmodes of a waveguide resonator with small curvature mirrors is presented. Field differential equations are derived. Eigenfunctions and eigenvalues are given approximately. Cut-off curvatures are obtained. A criterion which can help to distinguish between a waveguide laser resonator and an open Fabry-Perot one is proposed     

Optical arbitrary waveform generation based on an array of tunable apodized waveguide Bragg gratings

A structure of optical arbitrary waveform generation (OAWG) based on an array of tunable apodized waveguide Bragg gratings (WBGs) is proposed. The WBGs array on lithium niobate (LN) consists of several apodized gratings, waveguides and electrodes deposited on both sides of gratings and waveguides. The properties of OAWG are analyzed using transfer matrix method. Due to the electro-optic effect of LN, the amplitude and phase of incident light source are controlled via adjusting the voltages on electrodes. Consequently, the optical pulses with different waveforms are obtained and the amplitude is linearly tuned. In addition, voltages compensating amplitude and phase distortion are demonstrated.     

Measurement of optical nonlinearity in silicon rich nitride waveguide ring resonators

The optical nonlinearities of amorphous silicon rich nitride corresponding to /spl chi//sup (3)/ in a static electric field have been measured by tracking wavelength shifts in the resonances of optical waveguide ring resonators as a function of an applied electrical field. The magnitude of the nonlinearity measured agrees well with expected values.     

Optical transmission characteristics of fiber ring resonators

We present the results of an experimental investigation of the transfer characteristics of a fiber ring resonator for various values of the resonator finesse. In particular, we measure the spectral dependence of the intensity transmission and the induced phase shift in the undercoupled, critically coupled, and overcoupled regimes. We also demonstrate tunable optical (true time) group delay via a fiber ring resonator and show that a high finesse is unnecessary. Our laboratory results are in excellent agreement with theoretical predictions.     

用波导模求解具有侧反射面的光学谐振腔

使用侧面抛光的激光棒的激光器能减小热光路畸变的影响,这是因为它构成一类特殊的谐振腔——带有侧反射面的腔。本文用波导模式的迭加求得了这种腔模式的解析表达式。     

平板宽波导谐振腔耦合损失理论研究

计算了平板宽波导谐振腔中ＥＨ１１模的耦合损失，结果表明存在两种特定结构使耦合损失最小。     

脊双模波导滤波器的分析及设计

介绍了一种能实现脊双模波导滤波器的新型结构,分析了其腔内模式的耦合极性,利用不同的耦合极性对频率响应的影响可实现具有一对传输零点的双模滤波器,也可实现无传输零点的双模滤波器.以相同脊谐振单元不同的放置方向组成的两种带通滤波器为例,利用AnsoftHFSS仿真得到了两种不同的频率响应,结果与理论分析一致.最后设计出了一个六阶三传输零点的双通带滤波器,带内插损均小于0.6 dB,回波损耗小于-15 dB.     

Optical bistability and differential amplification in nonlinearfiber resonators

Optical bistability and differential amplification, arising as a consequence of the nonlinear Kerr effect in fiber resonators, are considered in the present paper. A structure-independent transfer matrix method devised for linear operation is extended to account for nonlinear self-phase effects. General expressions are presented and applied to particular cases showing complete agreement with previously published results     

Optical signal generation at millimeter-wave repetition rates usingsemiconductor lasers with pulsed subharmonic optical injection

A new technique is presented and investigated systematically which generates optical signals at millimeter-wave repetition rates from a semiconductor laser, without the need for an intracavity saturable absorber. Optical pulses are generated from a long-cavity semiconductor laser with a repetition rate equal to its cavity resonant frequency by injecting short optical pulses at one of the cavity resonance subharmonics. A rate-equation model is proposed to explain the mechanism of this subharmonic optical injection method. Optical pulses with repetition rates of 35 and 56 GHz are generated using the proposed scheme from a semiconductor laser with a distributed Bragg reflector and a Fabry-Perot laser diode, respectively. The performance of the generated pulses is also evaluated in terms of detected RF power at the repetition frequencies, the subharmonic suppression ratio, phase noise, and timing jitter as a function of frequency detuning, injected optical power, laser bias current, and, finally, the subharmonic number. It is found that the generated optical pulses exhibit large subharmonic suppression ratio (>17 dB), large locking ranges >400 MHz, low levels of phase noise (~-93 dBc/Hz@10 kHz) and timing jitter (<0.41 ps over 100 Hz to 10 MHz), and large tolerance to variations in operating parameters     

Optical waveguide fabrication in neodymium-doped lithium niobate

Reports the realisation of high-quality, proton-exchanged optical waveguide structures in neodymium-doped lithium niobate. Measurements indicate that the presence of the neodymium does not alter the proton exchange rate, and the presence of the protons does not affect the emission and absorption spectra of the bulk material significantly. Such waveguides will permit the realisation of highly efficient semiconductor laser pumped amplifiers and laser structures integrated with electro-optic and/or acousto-optic elements