Yu-Ming Cui

Sellmeier equation for doubly Er/Mg-doped congruent LiNbO 3 crystals

Refractive indices of congruent LiNbO3 crystals codoped with 0.5 mol% Er2O3 and 0-5.0 mol% MgO were measured at room temperature in a wavelength range from 473 to 1536 nm using critical angle measurement and minimum deviation methods. For reference, measurements by the critical angle method were also performed on a congruent LiNbO3 and a congruent MgO (5 mol%):LiNbO3. The measured data are compared with previously reported theoretical and/or experimental results of pure and MgO-doped LiNbO3, especially with the results predicted by the MgO content-related Sellmeier equation (SE) reported by Schlarb and Betzler. It is shown that the Schlarb and Betzler SE consistently predicts a lower index, by as much as 4×10−3, than what is actually measured by the authors for both congruent LiNbO3 and for MgO:LiNbO3, whether it is codoped with Er or not. To check the Er doping effect, measurements by the critical angle method were also performed on some congruent LiNbO3 crystals singly doped with 0-1.0 mol% Er2O3. The results show that Er doping has no measurable effect. It is concluded that there may be a systematic error as one uses the Schlarb and Betzler SE to predict the index of the undoped, only MgO-doped, and Er/Mg-codoped crystals. The Schlarb and Betzler SE parameters are refined to fit our experimental data. The corrected version of the SE suitable for MgO:LiNbO3 with or without Er doping is given.

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.

Diffusivity of Er3+ into LiNbO3 as a function of stoichiometry

Diffusivity of Er3+ into LiNbO3 crystal has been studied as a function of Li2O content and crystal orientation. The Li2O content in single-crystal LiNbO3 plates was adjusted by Li-rich vapor transport equilibration (VTE) technique. Five X-cut and five Z-cut congruent substrates were VTE treated at first at 1100 °C for different durations ranging from 6 to 74 h, and then were subjected to a special post-VTE anneal procedure at the same temperature for 60 h to obtain homogeneous Li2O content. The Li2O content was determined from the measured fundamental optical absorption edge. Its homogeneity is verified by measuring the optical absorption edge as a function of the crystal thickness. After the composition characterization, the substrates were coated with 45 nm thick Er film and annealed at 1130 °C for 40 h in argon atmosphere. The Er3+ profile was analyzed by secondary ion mass spectrometry. The results show that the Er3+ diffusivity decreases monoexponentially with the increase in the Li2O content in both...

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.

Surface Etching of MgO : LiNbO3 Crystal by Ti Metal for Integrated Optics

Surface etching of a MgO-doped LiNb0 3 crystal is demonstrated by annealing a sandwich structure formed by Mg:LiNb0 3 /Ti film/Mg:LiNb0 3 at 1050-1100°C in a wet O 2 atmosphere. The etching depth, raised Ti layer height and surface roughness were studied as a function of initial Ti film thickness, annealing temperature, and duration. The results show that the maximum etching depth can reach 260 nm while the surface roughness is < 5 nm. The features of the raised Ti layer height and surface roughness of the etched surface and raised Ti layer are discussed on the basis of the Ti diffusion mechanism. Combined studies of X-ray single-crystal diffraction, Raman scattering, energy-dispersive X-ray, waveguiding characteristics, surface refractive index, and secondary-ion mass spectrometry show that the etched surface not only retains the LiNbO 3 crystalline phase and the original crystal composition but is also Ti-free. An etching mechanism based upon an electrochemical reaction process is proposed. The MgO doping effect on the etching rate and surface roughness is discussed and explained in terms of the MgO doping effect on Ti solubility. A comparison of the +Z and -Z surface etching is made. Finally, the present method is compared with other etching techniques and its possible application is suggested.