Itandehui Gris-Sánchez

The photonic lantern

Photonic lanterns are made by adiabatically merging several single-mode cores into one multimode core. They provide low-loss interfaces between single-mode and multimode systems where the precise optical mapping between cores and modes is unimportant.

Adiabatically-tapered fiber mode multiplexers

Simple all-fiber three-mode multiplexers were made by adiabatically merging three dissimilar single-mode cores into one multimode core. This was achieved by collapsing air holes in a photonic crystal fiber and (in a separate device) by fusing and tapering separate telecom fibers in a fluorine-doped silica capillary. In each case the LP01 mode and both LP11 modes were individually excited from three separate input cores, with losses below 0.3 and 0.7 dB respectively and mode purities exceeding 10 dB. Scaling to more modes is challenging, but would be assisted by using single-mode fibers with a smaller ratio of cladding to core diameter.

Highly-efficient, octave spanning soliton self-frequency shift using a specialized photonic crystal fiber with low OH loss

We report the first demonstration of efficient, octave spanning soliton self-frequency shift. In order to achieve this we used a photonic crystal fiber with reduced OH absorption and widely spaced zero-dispersion wavelengths. To our knowledge, this is the largest reported frequency span for a tunable, fiber-based source. In addition, we observe the generation of light above 2 μm directly from a Ti:Sapphire laser in the form of Cerenkov emission by the soliton when the red-shift saturates at the edge of the anomalous dispersion region.

Reducing spectral attenuation in small-core photonic crystal fibers

We describe a modified fabrication process to reduce spectral attenuation in highly nonlinear photonic crystal fibers (PCF) by reducing the effect of OH- content in the silica glass. In particular we show outstanding results for small core sizes of 2μm diameter including an attenuation of 10dB/km at the OH- peak wavelength of 1384nm, by annealing the preform prior to the fiber draw.

Efficient photonic reformatting of celestial light for diffraction-limited spectroscopy

The spectral resolution of a dispersive astronomical spectrograph is limited by the trade-off between throughput and the width of the entrance slit. Photonic guided wave transitions have been proposed as a route to bypass this trade-off, by enabling the efficient reformatting of incoherent seeing-limited light collected by the telescope into a linear array of single modes: a pseudo-slit which is highly multimode in one axis but diffraction-limited in the dispersion axis of the spectrograph. It is anticipated that the size of a single-object spectrograph fed with light in this manner would be essentially independent of the telescope aperture size. A further anticipated benefit is that such spectrographs would be free of ‘modal noise’, a phenomenon that occurs in high-resolution multimode fibre-fed spectrographs due to the coherent nature of the telescope point spread function (PSF). We seek to address these aspects by integrating a multicore fibre photonic lantern with an ultrafast laser inscribed three-dimensional waveguide interconnect to spatially reformat the modes within the PSF into a diffraction-limited pseudo-slit. Using the CANARY adaptive optics (AO) demonstrator on the William Herschel Telescope, and 1530 ± 80 nm stellar light, the device exhibits a transmission of 47–53 per cent depending upon the mode of AO correction applied. We also show the advantage of using AO to couple light into such a device by sampling only the core of the CANARY PSF. This result underscores the possibility that a fully optimized guided-wave device can be used with AO to provide efficient spectroscopy at high spectral resolution.

New multicore low mode noise scrambling fiber for applications in high-resolution spectroscopy

We present a new type of multicore fiber (MCF) and photonic lantern that consists of 511 individual cores designed to operate over a broadband visible wavelength range (380-860nm). It combines the coupling efficiency of a multimode fiber with modal stability intrinsic to a single mode fibre. It is designed to provide phase and amplitude scrambling to achieve a stable near field and far field illumination pattern during input coupling variations; it also has low modal noise for increased photometric stability. Preliminary results are presented for the new MCF as well as current state of the art octagonal fiber for comparison.

Time-Dependent Degradation of Photonic Crystal Fiber Attenuation Around OH Absorption Wavelengths

We present a study of the time-dependent degradation of attenuation in Photonic Crystal Fibers in the wavelength region from 1350 nm to 1450 nm. Changes in spectral attenuation were monitored over 16 weeks of exposure to a laboratory environment in different solid core PCFs as well as in a hollow-core bandgap fiber. Increasing spectral attenuation was observed at 1364 nm and at 1384 nm, wavelengths corresponding to known OH absorption features in silica. We also observe the appearance of a broad attenuation peak around 1398 nm. The observed degradation is shown to decrease exponentially from the ends of the fiber, and is attributed to ingress of contaminants from the fiber ends. This attribution is supported by measurements on a fiber stored with sealed ends.

The airy fiber:an optical fiber that guides light diffracted by a circular aperture

We have designed and made an optical fibre that guides an approximate Airy pattern as one of its guided modes. The fibres attenuation was 11.0 dB/km at 1550 nm wavelength, the match between the fibres mode and the ideal infinite Airy pattern was 93.7%, and the far field resembled a top-hat beam. The guidance mechanism has strong similarities to photonic bandgap guidance.

Characterizing the variation of propagation constants in multicore fiber

We demonstrate a numerical technique that can evaluate the core-to-core variations in propagation constant in multicore fiber. Using a Markov Chain Monte Carlo process, we replicate the interference patterns of light that has coupled between the cores during propagation. We describe the algorithm and verify its operation by successfully reconstructing target propagation constants in a fictional fiber. Then we carry out a reconstruction of the propagation constants in a real fiber containing 37 single-mode cores. We find that the range of fractional propagation constant variation across the cores is approximately ± 2 × 10(-5).

Multiplexed Single-Mode Wavelength-to-Time Mapping of Multimode Light

When an optical pulse propagates along an optical fibre, different wavelengths travel at different group velocities. As a result, wavelength information is converted into arrival-time information, a process known as wavelength-to-time mapping. This phenomenon is most cleanly observed using a single-mode fibre transmission line, where spatial mode dispersion is not present, but the use of such fibres restricts possible applications. Here we demonstrate that photonic lanterns based on tapered single-mode multicore fibres provide an efficient way to couple multimode light to an array of single-photon avalanche detectors, each of which has its own time-to-digital converter for time-correlated single-photon counting. Exploiting this capability, we demonstrate the multiplexed single-mode wavelength-to-time mapping of multimode light using a multicore fibre photonic lantern with 121 single-mode cores, coupled to 121 detectors on a 32 × 32 detector array. This work paves the way to efficient multimode wavelength-to-time mapping systems with the spectral performance of single-mode systems.