Optics/Scanner

From OpenLidar-Wiki
Jump to: navigation, search

Optics/Scanner documentation in PDF form: File:Optics & Scanner Module.pdf


Synopsis

The optics/scanner module is designed to alter the original laser beam into radiation with desired specification that can be sent to the target and received by the detector properly. It consists two sub modules, the optics and scanner module, the latter of which is optional and depends on the application.

Glossary of Terms

1. AOM: Acousto-optic modulator

2. EDFA: Erbium-doped fiber amplifier

3. PBS: Polarising beam splitter

Design Requirements

This section includes the objectives and constraints of the Optics and Scanner modules.

1. Must be suitable for the range of optical power delivered by the laser

2. Must be durable enough to withstand the operating conditions of the lidar

Safety

This section describes the safety concerns of the Optics and Scanner modules, as well as suggestions for mitigating any possible risks.

The safety concern of the Optics/scanner module centers on the chance of incoming radiation being redirected into the eyes of a bystander. Therefore, any radiation paths throughout the module must be completely sealed from the outside world. This includes both the transmitted beam path and the received beam path.

High Level Overview

This section will discuss the main functions of the Optics and Scanner modules and their constituent components.

Optics & Scanner System Diagram.jpg

Figure 1: System diagram of the Optics/Scanner module

The Optics and Scanner modules is separated into two major categories, the transmitted beam and the received beam. The transmitted beam category includes all the optical devices used in the process involving the laser beam being emitted from the laser source and hitting the target. A list of possible optical devices that can be used during this process is shown in Figure 1. The scanner part is also included in this category but it is optional. This way, the user will have the option to decide whether the ability to scan should be included in the system or not. The received beam category includes all the optical devices used in the process involving the laser beam being backscattered from the target and being received by the detector. Figure 1 shows a list of optical devices that can be used during this phase.

Low Level Information

This section will discuss the details of the Optics/Scanner module, including suggestions that may be implemented to accomplish its roles in the lidar system.

This section will discuss the function of each component and provide details on each part. Mirrors are not included in the module, but are commonly used to alter the beam path or reduce the optical design size, which should be considered in the user’s system if necessary.

A list of possible optical devices used during the transmitted beam phase, not including the scanner, contains beam splitter, AOM, EDFA, circulator, filter, and PBS. A beam splitter splits the incident laser beam into two or more beams with or without equal optical power(1), and it is required in the lidar systems to split the original laser beam into local oscillator and the transmitted beam that will be sent to the atmosphere. To determine the direction of the frequency shift and amplify the optical signal, AOM and EDFA can be used respectively. Also, a circulator is used to separate optical signals that travel in the opposite direction in the optical fiber(3), while a filter is used to transmit only a specific wavelength of laser radiation and absorb radiation at other wavelengths(4). Finally, a PBS can divide the unpolarized light into two polarized lights according to the polarization direction(5).

The steering of laser beam can be one-dimensional or two-dimensional. The angular resolution and scanning range will vary based on the rotation and movement of different types of mirrors used. For one-dimensional scanning, the rotation of a polygon mirror can lead to a periodic motion, and this scanning motion is generally controlled by some electronics. As for two-dimensional scanning, it can be done by either rotating one mirror along two axes or reflecting the beam onto two mirrors that are mounted on orthogonal axes. In this case, either flat mirrors or polygon mirrors can be used(6). On the other hand, a list of possible optical devices used during the received beam phase includes hole mirror, telescope, and optical fiber. A hole mirror allows the backscattered beams to transmit through the system, and a telescope is used to collect the backscattered beams from a range of incident angle. For data transmission from the received beam to the photodetector, an optical fiber can be used.

Interfaces

Optics & Scanner Dependency Map.jpg

Figure 2: Dependency Map of Optics/Scanner module; details in the table below

Figure 2 shows the dependencies of the Control Module with the rest of the lidar system. The inputs and outputs are described in detail below. The descriptions are colour coded for ease of reading and transferring from diagram to text.

Inputs Outputs
Power

- Power to operate any optical devices needed

Control

- Module atmosphere and other relevant sensor data

Housing

- Physical connection to allow radiation to escape the system

Housing

- Laser beam through optics hole in housing

Laser

- Laser beam to be sent to the target

Detector

-Laser beam (through a beam splitter) to act as a local oscillator

-Backscattered (doppler shifted) radiation

Table 1: Inputs and outputs of Optics/Scanner module

Progress

This module is currently in the abstract definition phase.

Testing

Type description of testing on module here.

Comments

Software and power diagrams should be created as needed.

Optics module colour (Hex code): #1155cc

Scanner module colour (Hex code): #784004

Revision History

Description of Work Date Author
Document started 21.07.15 Alan Yeh
Added High Level Overview, Low Level Overview, System Diagram, Dependency Map, Interfaces 23.07.15 Alan Yeh
General edits to grammar and style 31.07.15 Joshua Calafato, Katherine Maul, Frank Modruson IV, Alan Yeh
Added References 02.08.15 Alan Yeh
Added Hex codes, other minor edits 12.08.15 Frank Modruson IV

References

1. Paschotta, R. (n.d.). In RP-Photonics.com. Beam Splitters. Retrieved August 2, 2015 from http://www.rp-photonics.com/beam_splitters.html

2. Paschotta, R. (n.d.). In RP-Photonics.com. YAG Lasers. Retrieved August 2, 2015 from http://www.rp-photonics.com/yag_lasers.html

3. Optical circulator. (n.d.). In Wikipedia.org. Retrieved August 2, 2015 from https://en.wikipedia.org/wiki/Optical_circulator

4. Optical Filters. (n.d.). In EdmundOptics.de. Retrieved August 2, 2015 from http://www.edmundoptics.de/optics/optical-filters/

5. Paschotta, R. (n.d.). In RP-Photonics.com. Polarizers. Retrieved August 2, 2015 from http://www.rp-photonics.com/polarizers.html

6. Laser scanning. (n.d.). In Wikipedia.org. Retrieved August 2, 2015 from https://en.wikipedia.org/wiki/Laser_scanning