Thin Film System Introduction

Thin Film System Introduction

This chapter introduces the fundamentals of thin film optical systems used in OSC Low-E software, helping users understand various calculations and operations.

Film Stack Structure

The OSC Low-E film stack structure consists of five main parts. Light propagates from bottom to top, passing through each layer in sequence:

1. Incident Medium: The medium where light enters, typically air
2. Front Stack: Thin film layers coated on the front surface of the substrate
3. Substrate: The glass base that supports the thin films
4. Back Stack: Thin film layers coated on the back surface of the substrate
5. Exit Medium: The medium where light exits, typically air

Layer Numbering Convention

Important

OSC Low-E strictly follows these physical definitions, regardless of the light incidence direction:

• Layer 1: Always the layer closest to the Substrate
• Layer N: Always the layer farthest from the Substrate (closest to incident/exit medium)

Front Stack and Back Stack Definitions:

• Front Stack: Located on the front surface of the substrate. Layer 1 is adjacent to the substrate, Layer N is adjacent to the incident medium
• Back Stack: Located on the back surface of the substrate. Layer 1 is adjacent to the substrate, Layer N is adjacent to the exit medium

Spectrum Calculation Types

OSC Low-E supports 12 basic spectrum calculation types, divided into three categories:

A. Front Stack Design

Considers only Incident Medium + Front Stack + Substrate.

Type	Name	Description
Forward Reflectance	FrontDesignRfront	Light enters from incident medium, measures reflectance R
Forward Transmittance	FrontDesignTfront	Light enters from incident medium, measures transmittance T
Backward Reflectance	FrontDesignRback	Light enters from substrate, measures reflectance R'
Backward Transmittance	FrontDesignTback	Light enters from substrate, measures transmittance T'

B. Back Stack Design

Considers only Substrate + Back Stack + Exit Medium.

Type	Name	Description
Forward Reflectance	BackDesignRfront	Light enters from substrate, measures reflectance R
Forward Transmittance	BackDesignTfront	Light enters from substrate, measures transmittance T
Backward Reflectance	BackDesignRback	Light enters from exit medium, measures reflectance R'
Backward Transmittance	BackDesignTback	Light enters from exit medium, measures transmittance T'

C. Whole Stack Design

Considers the complete system: Incident Medium + Front Stack + Substrate + Back Stack + Exit Medium.

Type	Name	Description
Forward Reflectance	WholeStackRfront	Light enters from incident medium, measures total reflectance R
Forward Transmittance	WholeStackTfront	Light enters from incident medium, measures total transmittance T
Backward Reflectance	WholeStackRback	Light enters from exit medium, measures total reflectance R'
Backward Transmittance	WholeStackTback	Light enters from exit medium, measures total transmittance T'

Tip

Whole stack calculations treat the "substrate thickness" as a finite thickness layer, thus including incoherent effects (interference effects are averaged out) of the substrate.

Related Terms

For more terminology, please refer to the Glossary.