51 research outputs found
Characterizing the variation of propagation constants in multicore fibre
We demonstrate a numerical technique that can evaluate the core-to-core
variations in propagation constant in multicore fibre. 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 fibre. Then we carry out a reconstruction of the
propagation constants in a real fibre containing 37 single-mode cores. We find
that the range of fractional propagation constant variation across the cores is
approximately .Comment: 17 pages; preprint format; 5 figures. Submitted to Optics Expres
All-fibre wavefront sensor
We report on a tapered three-core optical fibre that can be used as a
tip-tilt wavefront sensor. In this device, a coupled region of a few
millimetres at the sensing tip of the fibre converts fragile phase information
from an incoming wavefront into robust intensity information within each of the
cores. The intensity information can be easily converted to linear wavefront
error over small ranges, making it ideal for closed loop systems. The sensor
uses minimal information to infer tip-tilt and is compatible with remote
detector arrays. We explore its application within adaptive optics and present
a validation case to show its applicability to astronomy.Comment: 7 pages, 6 figure
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Observing mode-dependent wavelength-to-time mapping in few-mode fibers using a single-photon detector array
Wavelength-to-time mapping (WTM)—stretching ultrashort optical pulses in a dispersive medium such that the instantaneous frequency
becomes time-dependent—is usually performed using a single-mode fiber. In a number of applications, such as time-stretch imaging (TSI),
the use of this single-mode fiber during WTM limits the achievable sampling rate and the imaging quality. Multimode fiber based WTM
is a potential route to overcome this challenge and project a more diverse range of light patterns. Here, we demonstrate the use of a twodimensional
single-photon avalanche diode (SPAD) array to image, in a time-correlated single-photon counting (TCSPC) manner, the
time- and wavelength-dependent arrival of different spatial modes in a few-mode fiber. We then use a TCSPC spectrometer with a onedimensional
SPAD array to record and calibrate the wavelength-dependent and mode-dependent WTM processes. The direct measurement
of the WTM of the spatial modes opens a convenient route to estimate group velocity dispersion, differential mode delay, and the effective
refractive index of different spatial modes. This is applicable to TSI and ultrafast optical imaging, as well as broader areas such as
telecommunications
Trends in the full blood count blood test and colorectal cancer detection: a longitudinal, case-control study of UK primary care patient data [version 2; peer review: 2 approved, 1 not approved]
Background: The full blood count (FBC) is a common blood test performed in general practice. It consists of many individual parameters that may change over time due to colorectal cancer. Such changes are likely missed in practice. We identified trends in these FBC parameters to facilitate early detection of colorectal cancer. Methods: We performed a retrospective, case-control, longitudinal analysis of UK primary care patient data. LOWESS smoothing and mixed effects models were derived to compare trends in each FBC parameter between patients diagnosed and not diagnosed over a prior 10-year period. Results: There were 399,405 males (2.3%, n = 9,255 diagnosed) and 540,544 females (1.5%, n = 8,153 diagnosed) in the study. There was no difference between cases and controls in FBC trends between 10 and four years before diagnosis. Within four years of diagnosis, trends in many FBC levels statistically significantly differed between cases and controls, including red blood cell count, haemoglobin, white blood cell count, and platelets (interaction between time and colorectal cancer presence: p <0.05). FBC trends were similar between Duke’s Stage A and D colorectal tumours, but started around one year earlier in Stage D diagnoses. Conclusions: Trends in FBC parameters are different between patients with and without colorectal cancer for up to four years prior to diagnosis. Such trends could help earlier identification
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