Laser Characteristics and Applications

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Questions and Answers

What is the far-field pattern obtained by observing?

The emitted pattern on a screen 2 cm away

The emitted pattern in total darkness

The emitted pattern on a screen 11 cm away (correct)

The emitted pattern in direct sunlight

Which type of photodiode works in reverse bias?

Zener diode

Avalanche Photodiode (APD)

p-i-n photodiode (correct)

p-n photodiode

What is the condition of current in a photodiode when no light is incident?

It increases proportionally with distance

It is called the dark current (correct)

It remains unchanged regardless of light

It generates high voltage

What is measured when light is incident on a p-i-n photodiode?

Current varying with light intensity Signup and view all the answers

Which characteristic is used to characterize the optical detector?

Power vs Current characteristics Signup and view all the answers

What is a requirement for optical fiber connectors?

Should have low cost and low loss Signup and view all the answers

Which of the following best describes the structure of most optical connectors?

Plug-like in structure for alignment Signup and view all the answers

Which voltage is applied while testing an Avalanche Photodiode (APD)?

Up to 130V Signup and view all the answers

Which connector type typically has an insertion loss of approximately 1 dB?

SMA Signup and view all the answers

What is the primary function of a fusion splicer?

To permanently fuse two fibers together Signup and view all the answers

Which splicer method is specifically used for splicing ribbon fibers?

Mechanical splicer Signup and view all the answers

What aligns two fibers using an optical microscope in splicing?

Core alignment Signup and view all the answers

Which precaution should be taken to minimize bending losses?

Avoid bending the optical fiber Signup and view all the answers

What is a common feature of most optical connectors?

They are pre-attached to the fiber end Signup and view all the answers

What should be done to the fiber ends before splicing?

Clean thoroughly Signup and view all the answers

Which of the following connector types is NOT mentioned as a common connector type?

LC Signup and view all the answers

What does LASER stand for?

Light Amplification by Stimulated Emission of Radiation Signup and view all the answers

What is the primary use of semiconductor lasers?

As an optical source in optical communication Signup and view all the answers

In the context of laser operation, what is population inversion?

The condition where more atoms occupy the higher energy state E2 than the lower energy state E1 Signup and view all the answers

Which of the following accurately describes stimulated emission in a laser?

It occurs when an excited atom emits a photon of the same energy as the incoming photons Signup and view all the answers

What happens when the current applied to a semiconductor laser exceeds the threshold current?

A high coherent beam of light is emitted Signup and view all the answers

What role do mirrors play in a laser's optical cavity?

They maintain coherence and allow some light to escape as a laser beam Signup and view all the answers

What type of materials are typically used in semiconductor lasers?

Direct band gap materials with heavy doping Signup and view all the answers

Which type of emission occurs first when an atom absorbs energy?

Photon absorption Signup and view all the answers

Study Notes

Laser Characteristics

LASERS stand for Light Amplification by Stimulated Emission of Radiation.
Lasers are light amplifying devices, but they are difficult to use as pure amplifiers.
Lasers are mainly used as optical oscillators.
Semiconductor lasers are the most popular type of laser due to their low power, small size, and affordability.
Semiconductor lasers are also known as injection lasers or laser diodes.
They are made using heavily doped p⁺-n⁺ junction direct band gap materials.
Semiconductor lasers typically operate in the infrared region.
To achieve optical light amplification, more atoms must be in the higher energy level (E₂) than the lower energy level (E₁).
This condition is known as population inversion.
The optical cavity of a laser is formed using a pair of mirrors, one of which reflects the light, and the other allows some light to escape as the laser beam.
The emitted photons in a laser have similar phase and polarization, ensuring coherence.

Semiconductor Laser (Laser Diode LD)

Semiconductor lasers operate based on the same principle as general lasers.
The mirror structure is formed by cleaving the semiconductor crystal plane, creating a Fabry-Perot resonator.
When forward-biased, both spontaneous and stimulated emission occur in semiconductor lasers.
When the current applied exceeds the threshold current, a high coherent beam of light is emitted.
The characteristics of a laser diode are observed using a power meter and a current meter.
Spatial emission characteristics are measured by observing the emitted pattern on a diffusing screen at different distances from the diode.
Spectral characteristics are obtained by plotting power vs current characteristics while maintaining a fixed bias voltage.

Optical Detector

Optical detectors are devices that detect light.
They are classified into two types based on internal gain:
- Without Internal Gain:
  - p-n photodiode
  - p-i-n photodiode
- With Internal Gain:
  - Avalanche Photodiode (APD)
p-i-n photodiodes operate in reverse bias.
The current generated in a reverse-biased p-i-n photodiode is due to both thermally-generated minority carriers and photo-generated carriers.
The reverse-biased current is proportional to the light intensity.
A photodiode circuit typically consists of a photodiode connected to a resistance and two voltmeters.
The current is measured using an ammeter.
The current flowing in the circuit when no light is incident is called the dark current.
When light is incident, the current varies with the light intensity.

Study of Different Connectors

Optical fiber connectors are developed to meet various requirements in optical fiber communication.
Connectors should be easily attached, have low cost, and low loss.
Connectors are usually plug-like in structure and designed to align two optical fibers.
Common connector types include:
- ST
- SC
- SMA
- FCD
- FC
- D4
- DIN
- Biconic
Connectors are typically pre-attached to the fiber end, but some are available separately and need to be attached on-site.
The insertion loss of a connector is typically 1 dB per connector.

Splice Available Optical Fiber

Splicing is used to permanently join two optical fibers.
There are two types of splicers:
- Fusion Splicer: permanently fuses two fibers by applying an electric arc.
- Mechanical Splicer: aligns two fibers using epoxy resin or V-groove.
Fusion splicing is commonly used for fiber optic splicing in OSP and premises, compatible with single-mode and multimode fibers.
Two types of core alignment are used in fusion splicing:
- Core alignment (uses optical microscope)
- Cladding alignment (uses stationary V-grooves)
Mechanical splicing is often used for splicing ribbon fibers.

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Description

This quiz explores the fundamental concepts of lasers, including their definitions, types, and operational principles. Key topics such as semiconductor lasers, population inversion, and the optical cavity are covered to enhance understanding of this technology. Test your knowledge on how lasers amplify light and their common uses.