Monolithic 100 mW Yb waveguide laser fabricated using the femtosecond-laser direct-write technique

Abstract

A femtosecond laser-written monolithic waveguide laser (WGL) oscillator based on a distributed feedback (DFB) architecture and fabricated in ytterbium doped phosphate glass is reported. The device lased at 1033 nm with an output power of 102 mW and a bandwidth less than 2 pm when bidirectionally pumped at 976 nm. The WGL device was stable and operated for 50 hours without degradation. This demonstration of a high performance WGL opens the possibility for creating a variety of narrow-linewidth laser designs in bulk glasses.There is an ever-growing need for integrated optical devices for use in guided wave applications such as communications and sensing. International activity over the past 40 years has led to various technologies being used for the fabrication of such devices: ion exchange [1], silicon-on-insulator [2] and silica-on-silicon [3]. A relatively new fabrication method that also shows good promise in this field is that of ultrafast laser directwriting. It was shown in 1996 that focussed femtosecond laser pulses can induce a permanent refractive index change in dielectric media [4]. The index change is initiated by the electrons in the material absorbing energy from the radiation field via various nonlinear mechanisms. Because the absorption is nonlinear, material modification remains localised at the focal point where the laser intensity is highest. Hence, by translating the material through the focus of a femtosecond laser beam, a pathway of refractive index change can be produced using this technique. In many glasses femtosecond laser irradiation results in an increase in refractive index and hence waveguiding, while in crystalline hosts such as YAG and LiNbO 3 , waveguiding can only be achieved through suppressed cladding arrangements or induced stress fields as the index change is typically negative [5]. By varying the writing geometry, the material and femtosecond laser properties, 2D and 3D optical waveguide devices with different characteristics can be fabricated in the bulk of many transparent materials [6].Ultrafast laser writing has been successfully applied to active materials resulting in the creation of waveguide amplifiers and waveguide lasers (WGLs) [5,[7][8][9][10]. For example, a femtosecond laser encoded distributed feedback (DFB) colour center laser was reported in a LiF crystal operating in a pulsed mode at 704 nm using an optical parametric oscillator (OPO) as a pump [7]. However, the grating structure of this device was incoherent, the linewidth was significantly broader than that normally expected of DFB lasers and no output powers were reported. More recently, bulk glass WGL devices have been demonstrated using external fiber Bragg gratings (FBGs) to complete a cavity around a rare-earth doped waveguide amplifier [8,9]. This configuration is a bulk glass waveguide analogue to a fiber laser and allows for efficient pumping with 1

High slope efficiency and high refractive index change in direct-written Yb-doped waveguide lasers with depressed claddings

“…Waveguide lasers (WGLs) are ideal radiation sources for such photonic networks due to their small footprint, high efficiency and excellent beam quality which permit on-chip integration and low loss single-mode coupling [4]. In addition to CW-operation with narrow linewidth [5,6], in recent times femtosecond mode-locked WGL have attracted particular interest as they offer tens-ofGHz repetition rates [7].…”

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

“…Improved laser performance was obtained by Ams et al in a higher gain Yb-doped phosphate glass [42]. In this case, 102 mW of output power at 1032.6 nm in a 9.5-mm-long sample was achieved ( [62].…”

“…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 …”

Ultrashort Laser Pulses Machining

“…Although not a strict micromachining, permanent modification in the optical index of refraction have been extensively used to create light guiding structures in the bulk of transparent media [110,111]. The relative movement of the laser beam focus inside the material produces a pathway with cross section and index of refraction contrast suitable to guide light as waveguides embedded in the material bulk.…”