Caihe Chen

Theoretical analysis of guided mode and effective refractive index at 1.53 /spl mu/m in Ti:LiNbO/sub 3/ strip waveguides

An analysis of guided modes and effective refractive indexes in c-cut Ti-diffused LiNbO/sub 3/ strip waveguides has been performed at the wavelength 1.53 /spl mu/m by the variational method. Dependences of mode size and effective refractive index on initial Ti-strip width W, diffusion temperature T and initial Ti-strip thickness H have been calculated for several lower order modes. As compared the plots of the mode size with the previous published experimental results, an agreement in general behavior has been obtained. The single-mode and cutoff conditions were discussed numerically, which are very useful in optimizing and designing the Er:Ti:LiNbO/sub 3/ waveguide devices. In addition, several advantages of 1.48 /spl mu/m pumping were summarized.

Broadband Michelson fiber-optic accelerometer

A broadband (5-500 Hz) all-fiber-optic accelerometer was developed on the basis of Michelson interferometry, which is realized by a 3-dB single-mode fiber-optic beam splitter. On the distal endface of both interferometric arms of the splitter high-reflectance aluminum films were directly deposited to act as reflecting mirrors. The performance of a prototype of the accelerometer is examined. The results reveal that external stimuli can be truly sensed by the accelerometer, and the constraint level on lateral movement of the acceleration-sensitive mass is an important factor in determining the useful frequency bandwidth. The experimental results are compared with theoretical predictions.

Hybrid-integrated Michelson fiber optic accelerometer

A novel hybrid-integrated fiber optic accelerometer, based on Michelson interferometry, is developed. It makes use of a seismic mass suspended by a transduction fiber in a mass support. The Michelson interferometer is realized by a symmetrical double Y-branching wave- guide and three polarizers, which are monolithically integrated on an x-cut, y-propagating LiNbO3 substrate with dimensions of X3Y3Z52 33836 mm. On the distal endfaces of both interferometric arms, high- reflectance aluminum films are directly coated and serve as reflecting mirrors. An alternating current phase tracking (PTAC) homodyne scheme has been employed to process the signal. The performance of a proto- type of the accelerometer is characterized. The measured frequency spectrum is in good agreement with the theoretical prediction.

A theoretical study of a Ti-diffused Er:LiNbO/sub 3/ waveguide laser

A detailed theoretical procedure of determining the mode sizes of fundamental mode field distribution in a coaxially pumped Ti-diffused Er:LiNbO/sub 3/ waveguide laser has been described. The mode sizes, effective refractive indexes, effective pump area, and coupling efficiency as a function of the initial Ti stripe width W were numerically calculated for the waveguide with 95- and 100-nm initial Ti stripe thicknesses, respectively. The results indicated that the threshold pump power is severely affected by the stripe width, while slope efficiency is hardly changed as W; both show little difference between 95- and 100-nm stripe thickness. In addition, the stimulated emission cross section of Er/sup 3+/ in Er:LiNbO/sub 3/ channel waveguide versus the wavelength were calculated directly from its fluorescence spectra using the /spl beta/-/spl tau/ method. Subsequently, threshold pump power and slope efficiency were evaluated.

Michelson fiberoptic accelerometer

An all fiberoptic accelerometer, based on Michelson interferometry, has been developed theoretically and experimentally. It makes use of an oscillating mass suspended by a transduction fiber in a mass support. The interferometric configuration is formed by a 3 dB single-mode fiberoptic beam splitter, on two distal endfaces of which high-reflectance aluminum films were directly coated and served as reflecting mirrors. An ac phase tracking modulation–demodulation scheme has been employed to process the signal. The performance of a prototype of the accelerometer has been investigated, and the results indicated that the measured frequency spectrum is qualitatively consistent with the theoretical prediction, and the detected output wave forms are also in good agreement with that of the applied simulation signals. In addition, the constraint on the lateral movement of the acceleration-sensitive mass with two specific diaphragms has been experimentally verified, nevertheless, it needs to be optimized further.

Dependence of Ti-diffused Er:LiNbO/sub 3/ laser efficiency on waveguide fabrication parameters and pump wavelength

The mode size, effective pump area, and coupling efficiency as function of initial Ti-stripe width W, diffusion temperature T, and initial Ti-stripe thickness H in c-cut Ti-diffused Er:LiNbO/sub 3/ waveguide laser have been studied theoretically, taking into account optical pumping /spl lambda//sub p/=1.477 /spl mu/m and 0.98 /spl mu/m. The main features of the mode sizes in terms of these diffusion parameters were collected and, as compared with the experimental results, a qualitative agreement has been achieved. The effective pump areas exhibit both significant initial Ti-stripe width and diffusion temperature dependence, especially for W>9 /spl mu/m and T>1050/spl deg/C, whereas the initial Ti-stripe thickness can hardly give influence when pumping with /spl lambda//sub p/=0.98 /spl mu/m radiation. On the other hand, coupling efficiency is approximately unchanged with values 0.76-0.78 for /spl lambda//sub p/=1.477 /spl mu/m and 0.8-0.85 for /spl lambda//sub p/=0.98 /spl mu/m, indicating that there are no optimized values of these parameters to increase slope efficiency through coupling efficiency. Moreover, the 0.98 /spl mu/m pumping reveal lower threshold and higher coupling efficiency than 1.477-/spl mu/m pumping. Finally, the appropriate waveguide fabrication parameters were proposed for the fabrication of a more efficient laser.

A comparative analysis of TE and TM guided modes in Tidiffused Er:LiNbO3 waveguide lasers

Abstract A detailed comparative analysis of TE and TM guided-modes in Z-cut Ti-diffused Er:LiNbO3 strip waveguide lasers has been performed at laser emission wavelengths 1532, 1563, 1576 nm and pump wavelengths 1480 and 980 nm by the variational method. First, the mode size and corresponding effective refractive index at these five wavelengths as a function of initial Ti-strip width W, diffusion temperatures T, intial Ti-strip thickness H and diffusion time t were calcualted for several lower-order TE and TM modes; their characteristics and the single mode condition were discussed comparatively. Then, the plots of effective pump area and coupling efficiency between the laser and the pump modes under different pump and output mode polarizations were analysed. Finally, the coupling loss of a joint between the waveguide and a fibre in terms of these diffusion parameters were also calculated at these wavelengths. Numerical results are in good agreement with previously published experimental data.

Theoretical study of annealed proton-exchanged Nd:LiNbO/sub 3/ channel waveguide lasers with variational method

The controllable fabrication parameters, including anneal time, initial exchange time, channel width, dependences of TM/sub 00/ mode size, corresponding effective refractive index, effective pump area, and coupling efficiency between pump and laser modes in z-cut annealed proton-exchanged (APE) Nd:LiNbO/sub 3/ channel waveguide lasers were studied by using variational method. The effect of channel width on the surface index increment and the waveguide depth was taken into account. The features of mode size and effective refractive index were summarized, discussed, and compared with previously published experimental results. The effective pump area, which is directly proportional to threshold pump power, increases strongly, slightly, and very slightly with the increase of anneal time, channel width, and initial exchange time, respectively. However, the coupling efficiency, which is directly proportional to slope efficiency, remains constant (around 0.82) no matter what changes made to these parameters. The variation of the coupling loss between an APE channel waveguide and a fiber with these parameters for both laser (1085 nm) and pump (815 nm) wavelengths was also calculated. The calculated results indicate that the coupling loss decreases rapidly, slightly and very slightly with the increase of anneal time, channel width and initial exchange time, respectively.

Fabrication parameters optimization of Ti-diffused Nd:LiNbO 3 channel waveguide lasers

Abstract The variations of lower-order TM mode size and corresponding effective refractive index, effective pump area and coupling efficiency between pump and laser modes with the controllable fabrication parameters, i.e. initial Ti-strip width W, diffusion temperature T and initial Ti-strip thickness H in c-cut Ti-diffused Nd:LiNbO3 waveguide lasers have been calculated by using a variational method, taking into account both laser wavelength, 1085 nm, and pump wavelength, 815 nm. The main features of these curves were summarized and discussed in detail; consequently, the single-mode, fundamental mode cutoff and multimode conditions were presented and compared with the published experimental data. The effective pump area, directly proportional to threshold pump power, reveals a weak dependence on W in the considered range 4–16 μm and strong dependences on T and H in, respectively, the ranges studied 950–1100°C and 40–160 nm, while the coupling efficiency, directly proportional to slope efficiency, is hardly changed (with the values 0.82–0.85) with these parameters. Finally, appropriate diffusion parameters were proposed for the fabrication of a more efficient laser.

Structure design of Si-based M-Z interference acceleration seismic geophone

A novel Si-based MOEMS acceleration seismic geophone, based on M-Z interferometry, is present in this paper. In one silicon chip, several elements including four silicon beams,seismic mass, a polarizer, M-Z waveguide interferometer and acousto-optic phase modulator are integrated. The working principle and the optimization structure design of the acceleration seismic geophone are given. The simulation result performed in FEM software ANSYS agrees with the theoretical analysis well. The main design parameters of the geophone system is as following: resonance frequency: 1353 Hz; phase detection sensitivity ΔΦ/a: 1.2×10-4rad/m/s2.