Fig. 32. Experimental setup for laser test of dual-wavelength waveguide and cross-sectional microscopic image of depressed cladding waveguide with diameter of 100 μm shown in inset
[30] Fig. 33. Experimental results. Laser emission spectra at laser polarization angles of (a) 0°, (b) 45°, and (c) 90°, respectively; (d) relationship between output power and pump power at 812 nm pump and linear fit of experimental data indicated by solid line
[30] Fig. 34. Cross-section of depressed cladding structure fabricated in nonlinear Nd∶YCOB crystal
[78] Fig. 35. Experiments for waveguide lasing and self-frequency-doubling. (a) Schematic of end-face coupling system; (b) oscillation cavity for cladding waveguide lasing; (c) oscillation cavity for cladding waveguide self-frequency-doubling
[78] Fig. 36. Lasing and self-frequency-doubling performances of depressed cladding waveguides in Nd∶YCOB crystal. (a) Near-field intensity distributions of waveguide lasers at 1062 nm and boundaries of the guiding areas indicated within circles; (b) relationship between near-infrared laser output power and absorbed pump power for WG1, WG2, and WG3; (c) photograph of FP cavity employed for waveguide laser self-frequency-doubling experiments; (d) modal distributions of green lasers generated from WG1, WG2 and
Fig. 37. Depressed cladding waveguides fabricated in MgO∶PPSLT sample for second harmonic generation. (a)Schematic of fan-out pattern on MgO∶PPSLT sample and FLW process; (b) microscopic images of WG1-WG4
[9] Fig. 38. Waveguide-integrated light-induced quasi-phase matching structures. (a) Design of LiQPM depressed cladding waveguide; (b) modulation scheme of QPM grating structure inside waveguide core
[80] Fig. 39. Experimental results of temperature tuning for SHG of two kinds of LiQPM grating devices. (a) Dual-wavelength SHG; (b) multi-wavelength SHG
[80] Fig. 40. Optical microscopic images of superficial depressed cladding waveguides written by femtosecond laser in Nd∶YAG crystal. (a) Sectional view of semicircular waveguide; (b) sectional view of rectangular waveguide; (c) top view of rectangular waveguide; speckle patterns collected from output faces of (d) semicircular and (e) rectangular waveguides at 460 nm; (f) experimental setup for waveguide specklegram temperature sensor based on end-face coupling system in which thermo electric cooler used to c
Fig. 41. Effects of laser intensity and wavelength on sensitivity of different temperature sensors. (a)(c) Semicircular waveguide; (b)(d) rectangular waveguide
[33] Fig. 42. Waveguide Bragg gratings (WBGs) in ZBLAN glass. (a) Hexagonal lattice of points within core of waveguide and three-dimensional rendering of structure shown in inset (not to scale); (b) top-down differential interference contrast images at three different positions showing grating phase relation across core and reduction of grating contrast indicated apparently in close proximity to waveguide cladding (top profile)
[42] Fig. 43. Electro-optical tunable lithium niobate waveguide embedded with Bragg gratings. (a) Schematic of direct integration and characterization; (b) e light of circular waveguide structure with diameter of 15 μm; (c) multiscan Bragg grating with period of Λ=704 nm and upper and lower waveguide lines omitted for clear imaging; (d) cross section of polished WBG with integrated electrodes; (e) closed-circular waveguide; its modal profiles and insertion losses of (f) o light and (g) e light at λ<
Fig. 44. Bragg grating performance of depressed cladding waveguide. Reflection spectra for (a) o light and (b) e light as input light; (c) maximum spectral tuning of more than a peak width achieved with applied voltage of ±840 V for p light; (d) relative shift of central Bragg reflection maxima for s light (o light) and p light (e light) and high bandwidth operation for frequency test shown in inset
[13] Fig. 45. Mode field converter. (a) Schematic of fs-laser inscription process; (b) schematic of tapered waveguide; (c) model for implementation of tapered cladding with reduction factor of
dmax∶
dmin by decreasing track separation; (d) model for implementation of tapered cladding with reduction factor of
dmax∶(
dmin/2) by decreasing track separation and reducing number of tracks
[81] Fig. 46. Morphology and mode field characterization of mode field converter. (a) Microscopic image taken in transmission mode of 4∶1 tapered test structure fabricated with input radius of 24 μm and output radius of 6 μm (taper length
L shortened to well appreciate details); (b) modal profiles at output of 2∶1 and 4∶1 tapered waveguides at 633 nm (left) and 850 nm (right), respectively
[81] Fig. 47. Photonic devices based on Y-junctions. (a) Schematic of fabricated structures: straight waveguide, Y-junctions and Mach-Zehnder interferometer; (b) optical microscopic images of cross sections at different planes of Y-junctions and image at bottom indicating longitudinal view of splitting region and approximate positions of above images
[82] Fig. 48. Y-branch splitter based on superficial depressed-cladding waveguides. (a)-(e) Cross-sectional images and (f) top view of surface cladding waveguides; simulated refractive index distributions at cross sections of (g) input port, (h) joint port, and (i) output port, as well as (j) mode propagation process
[34] Fig. 49. 2×2 directional coupler based on depressed cladding waveguides. (a) Layout of interaction region with several cladding tracks skipped; (b) geometry of 2×2 waveguide coupler; (c) microscopic image of fabricated directional coupler obtained after stitching; (d) image of output facet of directional coupler; (e) intensity distribution at output facet of directional coupler with splitting ratio of 48∶52
[15] Fig. 50. 3×3 directional coupler based on depressed cladding waveguides. (a) Geometry of 3×3 directional coupler; (b) cross-sectional geometry of interaction region; (c) top view image of 3×3 coupler obtained after stitching; (d) microscopic image of end facet of 3×3 directional coupler; (e) intensity distribution at output facet of directional coupler with coupling distance of 14 μm
[15] Fig. 51. Schematic of depressed cladding waveguide directional coupler and transmission differential interference contrast microscopic images taken at different positions with dashed circles marking defects created by hard on/off switching of laser and output facet of directional coupler shown on right-hand side
[39] Fig. 52. Reconfigurable 2×2 directional coupler based on depressed cladding waveguides with ring cladding composed of 16 parallel damage tracks and circles tilted 10° with respect to
X axis
[14] Fig. 53. Electro-optically tunable directional coupler. (a) Top views of straight interaction region (middle) and two curved segments (left and right) of directional coupler; (b) partial top views of electrodes and directional coupler with interaction length of about 1.8 mm; (c) equipotential contour of electric field around electrodes;(d) splitting ratio versus voltage applied to electrode; (e) output modes at 1550 nm of coupler under three different voltages
[14