Electro–optical tunable waveguide embedded multiscan Bragg gratings in lithium niobate by direct femtosecond laser writing

Abstract

optical tunable Bragg gratings in lithium niobate fabricated by direct femtosecond laser writing. The hybrid design that consists of a circular type-II waveguide and a multiscan type-I Bragg grating exhibits low loss ordinary and extraordinary polarized guiding as well as narrowband reflections in the c-band of optical communications. High bandwidth tunability of more than a peak width and nearly preserved electro-optic coefficients of r(13) = 7.59 pm V(-1) and r(33) = 23.21 pm V(-1) are demonstrated.

Fabricating waveguide Bragg gratings (WBGs) in bulk materials using ultrashort laser pulses

“…In this case, the WBG refractive index contrast was photostable [68]. Waveguide lasers (WGLs) using this glass host showed a Multiscan WBGs were inscribed in lithium niobate very close to the threshold between types I and II modifications by Kroesen et al [49]. It was shown that, after thermal treatment at 250°C for 24 h, the WBG reflectivity decayed slightly; however, the spectral properties improved.…”

“…For comparison, Table 1 lists κ values for The duty cycle was fixed at 35%, whereas the writing pulse energy was varied. [21] PbP 1551 25 -Boro-aluminosilicate (Eagle2000) [22] PbP 1551 145 0.6 Boro-aluminosilicate (Eagle2000) [23] PbP 1550 472 0.5 Soda-lime [27] Two-step PbP 1577 14 -Fused silica [26] Modulated burst 1548 111 1.5 Er:Yb codoped phosphate [30] Modulated burst 1537 242 -Yb-doped phosphate [42] Modulated burst 1535 221 -Boro-aluminosilicate (Eagle2000) [31] Modulated burst 1551 713 -Fused silica [43] Modulated burst 1546 36 0.7 Boro-aluminosilicate (Eagle2000) [24] PbP 799 65 -Boro-aluminosilicate (Eagle2000) [28] Modulated burst 1552 157 -ZBLAN [29] PbP überstructure 1550 324 -Boro-aluminosilicate (Eagle2000) [44] Multiscan modulated burst 1563 177 -LiNbO 3 [45] Modulated burst stressors 1540 45 -Boro-aluminosilicate (Eagle2000) [41] PbP 648 136 -Boro-aluminosilicate (Eagle2000) [41] PbP 698 183 0.8 Boro-aluminosilicate (Eagle2000) [41] PbP 748 187 -Boro-aluminosilicate (Eagle2000) [41] PbP 798 163 -Fused silica [46] Modulated burst 1550 210 2.2 Fused silica [47] Modulated burst 1549 280 < 1 Chalcogenide (GLS) [48] Modulated burst 1551 179 -LiNbO 3 [49] Multiscan modulated burst (depressed clad) 1558 1230 1.52-3.51 Boro-aluminosilicate (Eagle2000) [50] Two-step PbP 1545 120 -Fused silica [25] PbP (waveguide bundle) 840 126 -Fused silica [25] PbP (waveguide bundle) 1550 220 1.6 Borosilicate (AF45) [51] Modulated …”

“…Gross et al demonstrated that WBGs consisting of periodic planes, constructed from a transverse hexagonal lattice of smaller point features, can be created inside a depressed cladding waveguide structure to control η ( Figure 10) [29]. Kroesen et al combined the multiscan technique and a cladding arrangement based on type II modifications to increase the WBG modal overlap factor [49]. Both the multiscan technique and the depressed cladding approach suffer from inflated fabrication times, and the increased number of inscription scans also subjects the WBG to changing environmental conditions during fabrication.…”

“…WBG birefringence may arise from the choice of substrate [49], laser-induced stresses [62], asymmetric waveguide modes [23], or self-aligned nanogratings [63,64]. The ULI technique gives researchers access to pathways of birefringence manipulation, thus opening an avenue to creating 3D polarisation-dependent/independent optical circuits.…”

“…The simplest way to generate a large WBG birefringence is to choose a birefringent host material from the outset. Kroesen et al used lithium niobate to create WBGs with a birefringence of 3.5 × 10 − 2 [49]. The majority of WBG demonstrations, however, have been reported in low birefringent materials.…”