Arturo Castillo-Guzman

Tunable multimode-interference bandpass fiber filter

We report on a wavelength-tunable filter based on multimode interference (MMI) effects. A typical MMI filter consists of a multimode fiber (MMF) spliced between two single-mode fibers (SMF). The peak wavelength response of the filter exhibits a linear dependence when the length of the MMF is modified. Therefore a capillary tube filled with refractive-index-matching liquid is used to effectively increase the length of the MMF, and thus wavelength tuning is achieved. Using this filter a ring-based tunable erbium-doped fiber laser is demonstrated with a tunability of 30 nm, covering the full C-band.

Widely tunable erbium-doped fiber laser based on multimode interference effect

A widely tunable erbium-doped all-fiber laser has been demonstrated. The tunable mechanism is based on a novel tunable filter using multimode interference effects (MMI). The tunable MMI filter was applied to fabricate a tunable erbium-doped fiber laser via a standard ring cavity. A tuning range of 60 nm was obtained, ranging from 1549 nm to 1609 nm, with a signal to noise ratio of 40 dB. The tunable MMI filter mechanism is very simple and inexpensive, but also quite efficient as a wavelength tunable filter.

A Core-Offset Mach Zehnder Interferometer Based on A Non-Zero Dispersion-Shifted Fiber and Its Torsion Sensing Application

In this paper, an all-fiber Mach-Zehnder interferometer (MZI) based on a non-zero dispersion-shifted fiber (NZ-DSF) is presented. The MZI was implemented by core-offset fusion splicing one section of a NZ-DSF fiber between two pieces of single mode fibers (SMFs). Here, the NZ-DSF core and cladding were used as the arms of the MZI, while the core-offset sections acted as optical fiber couplers. Thus, a MZI interference spectrum with a fringe contrast (FC) of about 20 dB was observed. Moreover, its response spectrum was experimentally characterized to the torsion parameter and a sensitivity of 0.070 nm/° was achieved. Finally, these MZIs can be implemented in a compact size and low cost.

Adaptable Optical Fiber Displacement-Curvature Sensor Based on a Modal Michelson Interferometer with a Tapered Single Mode Fiber

A compact, highly sensitive optical fiber displacement and curvature radius sensor is presented. The device consists of an adiabatic bi-conical fused fiber taper spliced to a single-mode fiber (SMF) segment with a flat face end. The bi-conical taper structure acts as a modal coupling device between core and cladding modes for the SMF segment. When the bi-conical taper is bent by an axial displacement, the symmetrical bi-conical shape of the tapered structure is stressed, causing a change in the refractive index profile which becomes asymmetric. As a result, the taper adiabaticity is lost, and interference between modes appears. As the bending increases, a small change in the fringe visibility and a wavelength shift on the periodical reflection spectrum of the in-fiber interferometer is produced. The displacement sensitivity and the spectral periodicity of the device can be adjusted by the proper selection of the SMF length. Sensitivities from around 1.93 to 3.4 nm/mm were obtained for SMF length between 7.5 and 12.5 cm. Both sensor interrogations, wavelength shift and visibility contrast, can be used to measure displacement and curvature radius magnitudes.

Ytterbium Fiber Laser Based on a Three Beam Optical Path Mach–Zehnder Interferometer

In this letter, a switchable ytterbium doped double cladding photonic crystal fiber (Yb-doped-DCPCF) laser based on a three optical path Mach-Zehnder interferometer (MZI) is presented. Here, the MZI with three-beam path was achieved by fusion splicing a segment of an Yb-doped-DCPCF between two pieces of single mode fibers. Moreover, in the proposed laser arrangement, the Yb-doped-DCPCF segment is acting simultaneously as the MZI and also as the gain medium. This laser can be switched to emit a single or double line by controlling the polarization state and it operates within the range from 1028 to 1033 nm. In addition, the laser emission has a linewidth of 0.07 nm and a single-mode suppression ratio of 40 dB. Finally, it is shown that the fiber laser arrangement is compact and robust and that requires a relativity simple fabrication procedure.

All-Fiber Tunable MMI Fiber Laser

We report on a novel tuning mechanism to fabricate an all-fiber tunable laser based on multimode interference (MMI) effects. It is well known that the wavelength response of MMI devices exhibits a linear dependence when the length of the multimode fiber (MMF) section. Therefore, tuning in the MMI filter is achieved using a ferrule (capillary tube of 127 μm diameter) filled with a liquid with a higher refractive index than that of the ferrule, which creates a variable liquid MMF. This liquid MMF is used to increase the effective length of the MMI filter and tuning takes place. Using this simple scheme, a tuning range of 30 nm was easily achieved, with very small insertion losses. The filter was tested within a typical Erbium doped fiber (EDF) ring laser cavity, and a tunable EDF laser covering the full C-band was demonstrated. The advantage of our laser is of course the simplicity of the tunable MMI filter, which results in an inexpensive tunable fiber laser.

Noncontact Optical Fiber Sensor for Measuring the Refractive Index of Liquids

A noncontact optical fiber sensor for measuring the refractive index of transparent liquids is proposed. It operates by calculating the path of a focused laser beam at 635 nm that travels across the boundaries of a liquid sample. The optical power Fresnel reflections are detected and, subsequently, the refractive index is determined as the ratio between the traveled beam paths when the liquid is deposited versus a reference without the liquid sample. Additionally, a mathematical analysis of the geometrical case is included. The theoretical data from our sensor are in good agreement with the experimental results. The resolution achieved by the sensor is better than 10−3 RIU.

Torsion sensor using a Mach-Zehnder interferometer

A novel torsion sensor based on a Mach-Zehnder interferometer is presented. The interferometer is made with a piece of Ytterbium doped photonic crystal fiber (YbDPCF) spliced between two single-mode fibers. The torsion sensitivity obtained is 0.05nm/º in a torsion range from 0° to 360° along with a sensitivity of 0.06dBm/º at specific wavelength. The interference fringes and torsion characteristics have been experimentally investigated and demonstrated. This compact fiber component with acceptable sensing performance makes its a good candidate for the measurement of numerous physical parameters.

Novel optical mux-demux module for fiber-optic communication applications

We demonstrated a novel design for a multi channel optical MUX/DEMUX module, which uses the principle of a Cassegrain-telescope. We carried out some optical simulations to show the feasibility to build up a multiplexer or de-multiplexer module for Dense Wavelength Division Multiplexing (4 channels). The set-up consists of a concave mirror that receives different beams which are then focused at the centre. For the case of a MUX-module, different radial positions enable injecting the system different wavelength inputs as the concave mirrors concentrates all the beams in one point (collector fibre). Moreover, for the case of a DEMUX-module, a bulk grating is positioned at one point between the concave mirror and the focal point of it, and when a stream of pulses with different wavelengths reaches this point, it automatically distributes the incoming signal in different radial positions (several collector fibers).

Intracavity absorption gas sensor in the near-infrared region by using a tunable erbium-doped fiber laser based on a Hi-Bi FOLM

We report an experimental study erbium-doped fiber laser for gas pressure detection in the L-band wavelength region by laser intracavity absorption spectroscopy. By using a high-birefringence fiber optical loop mirror as spectral filter within the ring cavity laser, the wavelength of the generated laser line is finely selected and tuned in a range of ~10 nm in order to select the wavelength where the gas absorption line is exhibited. Experimental results for detection of CO2 pressure with absorption at 1573.2 nm are shown and discussed. The proposed fiber laser sensor exhibits reliability and stability for gas detection with absorption in the L-band such as CO2, CO, and H2S.