Photonics Lab Instructional Videos

Align a Laser Beam Level to the Optical Table

Two methods for aligning a laser beam so that it propagates parallel to the surface of the optical table are demonstrated.

The first technique adjusts the pointing angle of a laser, whose tip and tilt can be adjusted. Using a ruler, the laser beam is leveled and directed along a row of tapped holes in the table.

Starting with this aligned beam, the technique for changing both the direction and the height of a beam from a fixed laser source is demonstrated. Two mirrors, which are set at different heights, direct the beam along another row of tapped holes in the table. The beam is then leveled at the height of the second mirror using two irises.

Components include a PL202 laser module, KM100 kinematic mounts, AD11NT adapter, BHM1 ruler, PF10-03-P01 mirrors, and IDA25 irises.

Date of Last Edit: Sept. 8, 2020

Avoid Screw-Length Pitfalls When Securing a Post Holder to a Table or Base

A common, unfortunate result of securing a post holder to a base or optical table is threads poking up through the bottom of the post holder. These exposed threads limit the height adjustment range offered by the post holder. Additional frustrations can result after rotating the post in the post holder, since this can unintentionally screw the post onto the exposed threads.

The solution is to keep screw length in mind when selecting a setscrew or cap screw to secure a post holder. In this video, observe consequences unfold due to threads projecting up from the bottom of the post holder, and learn techniques for overcoming this problem. The options of securing a post holder to a base or directly to the table are also compared.

Components used in this demonstration include Ø1/2" post holders, a BA2 base, Ø1/2" posts, cap screws, setscrews, and an iris.

Date of Last Edit: Sept. 24, 2020

Tune a Free Space Optical Isolator for Operation at the Laser Wavelength

Tuning a Faraday isolator ensures optimal transmission of optical power from the source, as well as effective suppression of reflections traveling back towards the source. Tuning is demonstrated using an IO-3-532-LP polarization-dependent free-space isolator with a 510 nm to 550 nm operating range, an R2T post collar, a PL201 linearly polarized and collimated 520 nm laser, a S120C silicon power sensor, and a PM400 power meter.

These optical isolators output linearly polarized light and provide best performance when the input beam is linearly polarized.

Always follow your institution's laser safety guidelines. Unlike the low-power source used in this demonstration, other laser sources may be damaged by back reflections. Many stray reflections, which can endanger colleagues and the laser, can be avoided by blocking the laser beam when it is not needed. 

Date of Last Edit: Sept. 10, 2020

Align a Linear Polarizer's Axis to be Perpendicular or Parallel to the Table

The beam paths through many optical setups are routed parallel to the optical table. When this is the case, the plane of incidence and the p-polarization are typically oriented parallel to the table's surface, while the s-polarization is perpendicular. Therefore, polarizers aligned to pass p- or s- polarized light effectively have their axes aligned to be parallel or perpendicular, respectively, to the table's surface.

A procedure for optically aligning the axis of a polarizer to be perpendicular to the optical table is discussed and demonstrated using optical power readings of light transmitted through the polarizer. Then, three options for aligning the axis of a polarizer to be parallel to the table are outlined. The method of crossed polarizers is demonstrated. Tips and tricks for obtaining more precise measurements are also shared.

Components used in this demonstration include a collimated laser, a polarizing beam splitter, linear polarizers, precision rotation mounts, an optical power sensor, and a power meter. There are also special appearances by a post collar and a ruler.

Date of Last Edit: Oct. 23, 2020

Cleave a Large-Diameter Silica Fiber Using a Hand-Held Scribe

An optical-quality end face can be achieved when a large-diameter optical fiber is manually cleaved using a hand-held scribe. The procedure is demonstrated using a multimode fiber with a 400 µm diameter core.

After stripping the protective polymer buffer from the end of the fiber and securing the fiber to a flat surface, a hand-held scribe is used to score the top surface of the fiber. The scribe should create a shallow nick in the fiber's cladding, away from the fiber's core. When cleaving smaller-diameter fibers, avoid creating too deep of a nick by reducing the scribing force and sweeping motion. In some cases, it is sufficient to lightly press a stationary scribe to the fiber. Applying a longitudinal tension to the fiber, across the nicked region, cleaves the fiber.

Also demonstrated is the visual evaluation of the end face quality using an eye loupe. A good quality end face will be a flat plane, perpendicular to the fiber's long axis. The light output from the cleaved end face was also observed on a viewing screen, and tips are shared for inspecting the output light distribution for information about the quality of the end face.

Components used in this demonstration include a tool for stripping the fiber buffer, a ruby scribe, an SMA bare fiber terminator, a 10X eye loupe, fiber grippers, a fiber-coupled LED, a viewing screen, and a quick-release adjustable fiber clamp on a free-standing platform.

Date of Last Edit: Nov. 3, 2020