Search results
Results from the WOW.Com Content Network
An optical attenuator, or fiber optic attenuator, is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. The basic types of optical attenuators are fixed, step-wise variable, and continuously variable.
The symptoms and signs associated with convergence insufficiency are related to prolonged, visually demanding, near-centered tasks. They may include, but are not limited to, diplopia (double vision), asthenopia (eye strain), transient blurred vision, difficulty sustaining near-visual function, abnormal fatigue, headache, and abnormal postural adaptation, among others.
o symptoms Zero symptoms ϕ Horizontal orthophoria θ Vertical orthophoria ⊕ Horizontal and vertical orthophoria OC's Optical centres Occ. Occupation OD oculus dexter (right eye) OH Ocular history OMB Oculo motor balance ONH Optic nerve head Oph Ophthalmoscopy OS oculus sinister (left eye) OU oculus uterque (both eyes) PD Pupillary distance
Attenuation is an important factor limiting the transmission of a digital signal across large distances. Thus, much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal. Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption.
Since the attenuation is defined as proportional to the logarithm of the ratio between () and (), where is the power at point and respectively. Using the cutback technique, the power transmitted through a fiber of known length is measured and compared with the same measurement for the same fiber cut to a length of approximately.
Impaired blood flow to the cells of the occipital lobe (ischemia, for example as caused by a TIA or Vertebrobasilar insufficiency) will lead to temporary visual problems; if the poor blood flow is sustained it will lead to cell death (infarction, for example as caused by a stroke) which may cause persistent visual problems. The main symptoms ...
This optic nerve must penetrate through the wall of the eye, and the hole to accommodate this is usually 20-30% larger than the nerve diameter. In some patients the optic nerve is nearly as large as the opening in the back of the eye, and the optic disc appears "crowded" when seen by ophthalmoscopy. A crowded disc is also referred to as a "disc ...
When the incident light beam is at Bragg angle, a diffraction pattern emerges where an order of diffracted beam occurs at each angle θ that satisfies: [3] = Here, m = ..., −2, −1, 0, +1, +2, ... is the order of diffraction, λ is the wavelength of light in vacuum, and Λ is the wavelength of the sound. [4]