[A CLASS PROJECT.]
- 1 aluminum mounting platform (the pizza pan!)
- 12 Chicago screws
- 2 FC/FC adapters
- 1 plastic loop form or wheel for mounting the fiber optic cable
- 1 100m single mode fiber optic cable with FC/UPC connectors
- 1 1.3 um analor IR laser ,fiber mountable, w/ ON/OFF switch
- 1 fiber mountable PIN diode deector / amplifier combo w/ zero control and 9V battery
- 1 multi-meter, 1MOhm input impedance
- 1 2x2 fiber optic coupler, single mode, w/ FC/UpC connectors
- 1 D Battery power supply
- 1 Phase controller (wheel) and mount
- 10 sets mounting clips and 6-32 screws
- (optional) rubber feet
(Special thanks to Skyhunt for easy assembly.)
The Sagnac Effect & the Journey of the Laser Light
(Go to Wikipedia for more information on the Sagnac Effect!)
The Sagnac Effect occurs when a laser light is split, and both beams are made to go the same path, but in different directions, in order to make the "ring". On return, however, both beams exit through the same door, but their collision causes interference - if both exit via a slit on a piece of paper, for instance, one would see overlapping hills and troughs of light, bright and dark bands rippling from the exit.
The Fun Part: So, when the platform that these lights are mounted upon rotates, the two beams shift, causing variations in the interference patterns. To measure the change from their initial position to their final position from each other, is to measure how far the vehicle with the gyroscope moved from their own default position. If a fighter-jet were to tip its nose downward by say, 5 degrees, the incredibly-sensitive gyroscope's lasers would shift, and the reading would come back to the pilot exactly (or almost exactly) how far they'd moved.
So, our laser light is beamed through the fiber-optic cable via the 1300nm IR laser, 1mW output - a cable composed on the inside of mirrors. The length and number of loops is directly responsible for the sensitivity of the gyroscope! The two wheels that control the phase of the light signal are simply smaller, additional loops that, when moved in a certain direction, help to stabilize the default position of that light (assumed 0) .
From there, the light is boosted by the PIN photo-diode amplifier, and likewise the "exit", where the acting interferometer (Multimeter or O-scope) picks it up and displays it.
Edit: Unfortunately, I'm out of time to put up a working video of the LRG's appearance at the Design Symposium, Spring 2014, but will definitely try for more pictures.
20140820 Wednesday: Equations
[From the Gyro Report]
Theory of Operation
The Sagnac interferometer/FOG works by having a light beam from a laser split into two light beams that travel in opposite directions, and are joined back together by a coupler. The difference in angular velocity between the two light beams causes different phase angles that are detected by the photo-diode. The photo-diode outputs a voltage dependent on the phase difference between the two light beams.
Δt = 4ΩA/c
2 , Δ fringe = 4ΩA/c
λ Sensitivity equation (for gyroscope)
Fiber-optic cable = 100m, radius (r) =0.16m, 100 turns ≈ 1 m circumference
1. Angular velocity (Ω) v/r = 6.25
2. Area (A) = 0.08m^2 * 100 = 8.04m^2
3. C = 3 * 10^8 m/s
4. Λ 1.3 * 10^6m^2
Δ fringe = 0.515, 360/(0.515 * 2) = 349.5°/s out of phase to in phase in rotation
Maximum voltage ≈ 850mV
Sensitivity = 349.5/850 = 0.41°/s/mV or .4°/s for 1mV on a meter.