Depressed Cladding Research Articles

Investigation of Refractive Index Profile Induced with Femtosecond Pulses into Neodymium Doped Phosphate Glass for the Purposes of Hybrid Waveguiding Structures Formation

The technique of writing depressed cladding waveguides into Nd:phosphate glass with relatively large mode field diameter in 2-line geometry was reported for the purposes of waveguiding structures formation. The easy to use and accurate technique of induced refractive index measurement was proposed, and it was shown the inefficiency of widespread indirect (numerical aperture) technique of refractive index measurement for such femtosecond written waveguides.

Widely tunable short-infrared thulium and holmium doped fluorozirconate waveguide chip lasers.

We report widely tunable (≈ 260 nm) Tm(3+) and Ho(3+) doped fluorozirconate (ZBLAN) glass waveguide extended cavity lasers with close to diffraction limited beam quality (M(2) ≈ 1.3). The waveguides are based on ultrafast laser inscribed depressed claddings. A Ti:sapphire laser pumped Tm(3+)-doped chip laser continuously tunes from 1725 nm to 1975 nm, and a Tm(3+)-sensitized Tm(3+):Ho(3+) chip laser displays tuning across both ions evidenced by a red enhanced tuning range of 1810 to 2053 nm. We also demonstrate a compact 790 nm diode laser pumped Tm(3+)-doped chip laser which tunes from 1750 nm to 1998 nm at a 14% incident slope efficiency, and a beam quality of M(2) ≈ 1.2 for a large mode-area waveguide with 70 µm core diameter.

Diode-laser pumping into the emitting level for efficient lasing of depressed cladding waveguides realized in Nd:YVO4 by the direct femtosecond-laser writing technique.

Depressed cladding waveguides have been realized in Nd:YVO(4) employing direct writing technique with a femtosecond-laser beam. It was shown that the output performances of such laser devices are improved by the reduction of the quantum defect between the pump wavelength and the laser wavelength. Thus, under the classical pump at 808 nm (i.e. into the (4)F(5/2) level), a 100-μm diameter circular waveguide inscribed in a 0.7-at.% Nd:YVO(4) outputted 1.06-μm laser pulses with 3.0-mJ energy, at 0.30 optical efficiency and slope efficiency of 0.32. The pump at 880 nm (i.e.directly into the (4)F(3/2) emitting level) increased the pulse energy at 3.8 mJ and improved both optical efficiency and slope efficiency at 0.36 and 0.39, respectively. The same waveguide yielded continuous-wave 1.5-W output power at 1.06 μm under the pump at 880 nm. Laser emission at 1.34 μm was also improved using the pump into the (4)F(3/2) emitting level of Nd:YVO(4).

LabVIEW Applications for Fiber-Optic Remote Test and Fiber Sensor Systems

This paper demonstrates applications of LabVIEW in automatic test measurement of fiber optic system.First,the LabVIEW applications in fiber optic system and the basics of instrument connectivity are presented.Then,the aspects of hardware communication to external instruments through GPIB and serial interfaces are analyzed.Next,self-calibrating automated characterization system for depressed cladding applications is demonstrated utilizing the LabVIEW’s GPIB interface. Results of the manual and automatic measurements and the analysis of the measurement trace obtained from the optical time domain reflectometer (OTDR) are shown.In the end,two applications of LabVIEW in fiber optic sensor system are discussed.

Efficient laser emission from cladding waveguide inscribed in Nd:GdVO(4) crystal by direct femtosecond laser writing.

We report on the fabrication of depressed cladding waveguides in Nd:GdVO(4) laser crystal by using femtosecond laser inscription. The cross section of the structure is a circular shape with a diameter of 150 μm. Under the optical pump at 808 nm, the continuous wave (cw) as well as pulsed (Q-switched by graphene saturable absorber) waveguide lasing at 1064 nm has been realized, supporting guidance of both TE and TM polarizations. The maximum output power of 0.57 W was obtained in the cw regime, while the maximum pulse energy of the pulsed laser emissions was up to 19 nJ (corresponding to a maximum average output power of 0.33 W, at a resonant frequency of 18 MHz). The slope efficiencies achieved for the cw and pulsed Nd:GdVO(4) waveguide lasers were as high as 68% and 52%, respectively.

Structural design and characteristics of dual-mode fibers with equalized group velocity.

We investigate how the index profile of a few-mode fiber (FMF) can be designed so that group velocities of the two lowest-order modes can be equalized at a normalized frequency, which is below the cut-off frequency of the LP21 mode. This can be achieved using a single-clad power-law profile with a sufficiently large profile exponent or a double-clad profile consisting of a graded-core surrounded by a sufficiently thick depressed inner cladding without index jump at their interface. The fabrication tolerances, effective index differences, intramodal dispersion differences, and effective mode areas of various single- and double-clad profiles are compared. The results show that, in comparison to single-clad fibers, double-clad fibers are capable of producing higher fabrication tolerances and reduced sensitivity of group delay difference to wavelength by three and two orders of magnitude, respectively. Our analyses provide insights into the design of FMFs, which will facilitate future development of high-capacity mode division long-haul transmission systems.

Two mode optical fibers with low and flattened differential modal delay suitable for WDM-MIMO combined system

We propose two mode optical fibers (TMFs) with minimally low differential modal delay (DMD) slope which are suitable for wavelength division multiplexing and multiple input multiple output (MIMO) combined transmission system. We designed and fabricated three different kinds of TMF, nearly zero-DMD (zTMF), positive-DMD (pTMF) and negative-DMD (nTMF) with a graded index core and a depressed inner cladding. We confirmed that the fabricated zTMF has DMD of below 15 ps/km in the C band and the fabricated pTMF and nTMF have the same degree of effective areas. We also confirmed that a DMD compensation line with a length of 100 km composed of pTMF and nTMF can successfully achieve the best properties of low DMD in the C + L band and low mode conversion.

Low scattering loss fiber with segmented-core and depressed inner cladding structure

In this paper, using the FEM method new low-loss fiber is proposed to minimize Rayleigh scattering with a segmented-core and depressed inner-cladding. The optical loss of the designed fiber is calculated based on Rayleigh scattering losses. Rayleigh scattering loss (RSL) has been estimated by Rayleigh scattering coefficient (RSC) and power distribution in the fiber. We have shown loss of less than 0.3dB/km at 1310nm, 0.18dB/km at 1550nm for step-index fibers which consist of conventional glass compositions such as SiO2, GeO2–SiO2, F–SiO2 while satisfying all of ITU-G.652.D attributes.

Fiber structure based on a depressed inner cladding fiber for bend, refractive index and temperature sensing

A fiber-optic structure based on a section of a double-clad fiber with depressed inner cladding is investigated for bend, refractive index and temperature sensing. The structure is formed by splicing a section of SM630 fiber between two standard fibers SMF-28. The operation principle relies on the sensitivity of cladding modes that are induced at a splice of fibers having different refractive index profiles. The mode structure of the double cladding fiber and the mechanism of formation of dips in the transmission spectra are discussed. The transmission spectra of the structure are measured for different curvatures of the inserted fiber section. The shift of dips to long wavelengths with increasing curvature of the fiber is observed and its dependence on the fiber section length and the direction of bending is investigated. The sensitivities of the spectral dips to the external refractive index and temperature are also measured.

Embedded optical waveguides fabricated in SF10 glass by low-repetition-rate ultrafast laser

Symmetric embedded waveguides were fabricated in heavy metal oxide SF10 glass using slit-shaped infrared femtosecond laser writing in the low-repetition frequency regime. The impact of the writing parameters on the waveguide formation in the transverse writing scheme was systemically studied. Results indicate that efficient waveguides can be inscribed in a wide parameter space ranging from 500 fs to 1.5 ps pulse duration, 0.7-4.2 μJ pulse energy, and 5 μm/s to 640 μm/s scan speed and pointing out the robustness of the photoinscription process. The refractive index profile reconstructed from the measured near field pattern goes up to 10(-3). In addition, propagation losses of the waveguides are tolerable, with the lowest propagation loss estimated at 0.7 dB/cm. With a 5 μm/s scan speed and 3.5 μJ pulse energy in a high-dose regime, few-mode guiding was achieved in the waveguide at 800 nm signal injection wavelength. This is due to a combination of increased refractive index in the core of the trace and the appearance of a depressed cladding.

Femtosecond laser micromachined optical waveguides in LiTaO3 crystal

AbstractBy using femtosecond laser micromachining, optical wave guides in both depressed cladding and dual‐line configurations have been produced in LiTaO3 crystal. The guiding properties and the thermal stability have been investigated for both geometries, which exhibit different performance. Depressed cladding waveguides support guidance along both extraordinary and ordinary index polarizations, while dual‐line waveguides support only extraordinary index polarization. Thermal annealing has been proved to be an effective method to reduce the propagation losses. For the cladding waveguide, the lowest propagation loss was as low as 0.38 dB/cm after the annealing treatment at 400 °C. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Femtosecond laser micromachining of lithium niobate depressed cladding waveguides

We report on the fabrication and characterization of femtosecond laser micromachined depressed cladding waveguides in lithium niobate crystal. The cladding structures support two-dimensional guidance of light from the visible to the mid-infrared spectral regimes. Particularly, single-mode propagation of light at a wavelength of 4 μm has been achieved for the waveguides with diameter of 50 μm. It is also found that the thermal annealing treatment reduces the propagation loss lower than 0.5 dB/cm at 1.064 μm, exhibiting good transmission properties for photonic applications.

Analysis and characterization of Er–Yb codoped-depressed inner cladding fiber

A 125 μm-diameter erbium-ytterbium-codoped single-mode fiber is reported. The utilization of depressed inner cladding guarantees the improvement of trade-off between the effective area and bending sensitivity compared to step-index profiles. Changes of cutoff wavelength, effective area, and macrobend loss under the influence of various structural parameters, and the balancing selection of core radius and subsidence layer width are investigated systematically. For the laboratory-made depressed inner cladding fiber, a macrobend loss of 0.06 dB/loop for a bending radius as tight as 10 mm was achieved, while maintaining an effective area of 164.22 μm² with intact single-mode properties at 1550 nm. The maximum small signal gain was achieved at 40.9 dB, and the gain fluctuation was less than 1 dB at the C-band. The fiber is suitable for high-power, small, portable, and handy optical fiber devices.

Fabrication and power scaling of a 17 W Cr:ZnSe waveguide laser

We report the fabrication and operation of a Cr:ZnSe buried channel waveguide laser operating at 2500 nm with a linewidth of 10 nm and a maximum power output of 1.7 W. Ultrafast laser inscription is used to fabricate the depressed cladding waveguide in a polycrystalline Cr:ZnSe sample. A thermal model is developed and predicts performance degradation at higher pump levels due to thermal quenching of the lifetime. This prediction is supported by the experimental results.

Efficient laser emission in diode-pumped Nd:YAG buried waveguides realized by direct femtosecond-laser writing

Laser emission at 1.06 and 1.3 μm under pumping with diode lasers was obtained from buried waveguides that were realized in a 0.7 at.% Nd:YAG single crystal by direct writing with a femtosecond laser. A depressed circular waveguide with a diameter of 110 μm yielded laser pulses at 1.06 μm with an energy of 1.4 mJ under the pump with pulses of 9.1 mJ energy at 807 nm; in continuous-wave operation, an output power of 0.54 W with optical to optical efficiency of 0.14 was achieved. Emission at 1.3 μm is demonstrated for the first time from such waveguides, with an energy of 0.4 mJ per pulse. Results for laser emission in other depressed cladding types and two-line-type waveguides are discussed.

Efficient 29 μm fluorozirconate glass waveguide chip laser

We report a large mode-area holmium-doped ZBLAN waveguide laser operating at 2.9 μm, which was pumped by a 1150 nm diode laser. The laser is based on ultrafast laser inscribed depressed cladding waveguides fabricated in uniformly rare-earth-doped bulk glass. It has a threshold of 28 mW and produced up to 27 mW of output power at an internal slope efficiency of approximately 20%.

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

We report the first Yb:ZBLAN and Yb:IOG10 waveguide lasers fabricated by the fs-laser direct-writing technique. Pulses from a Titanium-Sapphire laser oscillator with 5.1 MHz repetition rate were utilized to generate negative refractive index modifications in both glasses. Multiple modifications were aligned in a depressed cladding geometry to create a waveguide. For Yb:ZBLAN we demonstrate high laser slope efficiency of 84% with a maximum output power of 170 mW. By using Yb:IOG10 a laser performance of 25% slope efficiency and 72 mW output power was achieved and we measured a remarkably high refractive index change exceeding Δn = 2.3 × 10(-2).

Waveguides fabricated by femtosecond laser exploiting both depressed cladding and stress-induced guiding core

We report on the fabrication of stress-induced optical channel waveguides and waveguide splitters with laser-depressed cladding by femtosecond laser. The laser beam was focused into neodymium doped phosphate glass by an objective producing a destructive filament. By moving the sample along an enclosed routine in the horizontal plane followed by a minor descent less than the filament length in the vertical direction, a cylinder with rarified periphery and densified center region was fabricated. Lining up the segments in partially overlapping sequence enabled waveguiding therein. The refractive-index contrast, near- and far-field mode distribution and confocal microscope fluorescence image of the waveguide were obtained. 1-to-2, 1-to-3 and 1-to-4 splitters were also machined with adjustable splitting ratio. Compared with traditional femtosecond laser writing methods, waveguides prepared by this approach showed controllable mode conduction, strong field confinement, large numerical aperture, low propagation loss and intact core region.

Efficient mid-infrared Cr:ZnSe channel waveguide laser operating at 2486 nm

We report a Cr:ZnSe channel waveguide laser operating at 2486nm. A maximum power output of 285mW is achieved and slope efficiencies as high as 45% are demonstrated. Ultrafast laser inscription is used to fabricate the depressed cladding waveguide in a polycrystalline Cr:ZnSe sample. Waveguide structures are proposed as a compact and robust solution to the thermal lensing problem that has so far limited power scaling of transition metal doped II-VI lasers.

Large mode area waveguides with polarization functions by volume ultrafast laser photoinscription of fused silica

We present optical designs allowing large mode area light guiding by ultrafast laser photoinscription of bulk fused silica. If usual concepts are based on large core and depressed cladding, evanescently coupled multicore waveguides with coherent mode superposition can be effective solutions, where the introduction of nanostructured defects determines additional polarization functions.