FIG. II-3

(End view of fiber illustrating propagation of light ray)

Silica (glass) optical fiber has better light transmission characteristics (less loss) than plastic optical fiber (POF).  Silica fiber can tolerate higher temperatures than plastic fiber.  Plastic optical fibers are more flexible, less prone to  breakage, easier to fabricate into special assemblies, and lower in cost than glass fibers.

Typically, plastic optical fiber (POF) has a continuous operating temperature rating of   -55†C (-67F)  to 85†C (185F).   Most POFs can withstand up to 100†C (212†F) for short periods of time (less than 1 minutes).

As plastic optical fiber or glass fiber is bent, it’s transmission is reduced concurrently with the decrease of the bend radius. The minimum recommended bend radius is 10 times the fiber diameter.

The loss or attenuation of light in an optical fiber is determined by measuring the input power and output power as follows:

attenuation in dB = -10 log  (power out / power in)

The typical white light attenuation in plastic fibers is .2 to .25dB/m

The light transmission through optical fiber can be calculated from the attenuation specification:

  _{T  = 10}

III.  METHODS OF CREATING PLASTIC OPTICAL FIBER  (POF) BACKLIGHTING  DEVICES 

Light  emitted from the end of a fiber may be used on a backlighting device.  However, such end-light devices emit bright  spots of light from each fiber end making such devices less practical in  lighting surface areas than extracting light along the length of the fiber.  In order to extract light along the fiber  length, the travel of light within the fiber must be re-directed. 

Four  practical method causes light to escape over the length of a POF panel are: 

1.  Abraiding the fiber
2.  Terminating the fiber
3.  Sharply bending the  fiber
4.  Notching the fiber

FIG. III-1 (Typical plastic optical  fiber backlighting panel)

Plastic optical fiber backlights  utilizing the abrasion, termination, or notching process have fibers (typically  .010" dia.) configured side by side. These fiber lay-ups when adhered to a white reflective plastic film or a metal foil (See Fig. III-1) are referred to as panels or ribbons. The panels and ribbons are processed by abraiding, terminating or notching the fibers to cause light to escape evenly over the desired active area(s). 

1. ABRASION  METHODS

1.1.  Hot stamp abrasion process  (PolyStamp)

The "hot stamp" process is used to abrade one or more areas on a narrow plastic  optical fiber ribbon (See Fig. III-2). If more than one hot stamp is needed, the stamped locations furthest from  the light source are more aggressively abraided resulting in uniform light  emission from all the locations along the ribbon. Poly-Optical Products has trade-marked its  proprietary hot stamp process as PolyStamp®.

FIG. III-2  (Typical PolyStamp processed  backlighting ribbon)

1.2.  Large area abrasion process (UniGlo)(See Fig. III-3)

The  equipment required to hot stamp large fiber optic panels (greater than a few  square inches) is usually cost prohibited.  A large area abrasion process developed by Poly-Optical, called UniGlo®,  solves this problem by achieving the desired affect without a major capital  equipment investment. (Poly-Optical Products, Inc. patent numbers  5,312,569,  5,312,570 and 5,499,912).

FIG. III-3  (Typical UniGlo abrasion  processed backlighting panel) 

2.  FIBER TERMINATION PROCESS  (PolyGlo)

A  laser terminates specific fibers in a POF panel at locations where light  emission is desired

(See  Fig. III-4). These bright spots of light  usually require diffusion for backlighting applications and are not diffused for  decorative applications. Difusion is accomplished with a layer of translucent material such as plastic or elastomeric  rubber. Poly-Optical™s PolyGlo process (Poly-Optical Products, Inc. patents  5,097,396  5,226,105, 5,295,216 and  5,307,245) creates finely finished accurately placed lighting areas in specified  locations on a POF panel.

FIG. III-4  (Typical PolyGlo processed  backlighting panel). 

3.  FIBER BENDING METHOD

FIG. III-5 

Sharply bending plastic optical fibers, by weaving them into a POF panel (See  Fig. III-5)causes light to escape at the bend radii. This method, utilizing a special weaving process, produces backlighting panels that emit uniform spots of light at each bend. Poly-Optical's parent company, Lumitex, Inc., specializes in the woven method.

4.  Fiber notching process (PolyBright) (See Fig. III-6)

When  fiber or plastic rods or sheets are notched light is reflected out from the opposite side of the material. Light  uniformity is achieved by increasing the notch depth and frequency as the  distance from the light source increases.

PolyBright  is covered by Poly-Optical Product's patents 4,765,701 and 4,790,752

FIG. III-6  (Typical OptiGlo process)

IV.  POLYSTAMP^® BACKLIGHTING   

For narrow ribbons with short illuminated areas, Poly-Optical's PolyStamp process is used. A thin printed applique is adhered to the front of each PolyStamp area on the ribbon and a white reflective backplate is adhered to the opposite side. A typical PolyStamp ribbon with selectively illuminated areas is shown in Fig. IV-1.  

Preferred PolyStamp dimensioning and tolerances are shown in Fig. IV-1.

FIG. IV-1    (Typical PolyStamp  ribbon)

Appliques can  be designed to be white during daylight and in color when backlit. Standard print sizes for applique text is 8,  10, 12, and 14 point. Appliques can be installed right side up, upside down, vertical, or in combinations. Text orientation can be independent of applique orientation as shown in Fig. IV-2.

FIG. IV-2

V. UNIGLO®  BACKLIGHTING

FIG.  V-1  (Typical UniGlo backlighting  panel)

Poly-Optical's patented UniGlo  technology is a proprietary abrasion process that causes plastic optical fiber  panels to glow uniformly. Most UniGlo  processed backlighting panels are constructed of .010" diameter plastic optical  fibers. Utilizing a reflective backing,  the panel can be as thin as .013" for a single layer device. Two or more layers provide greater brightness and improved uniformity. This technology  is ideal for backlighting membrane switches, LCDs, panels, control consoles, PRNDL™s, keyless entry, machine vision, man-machine interface, elastomeric  keypads, courtesy lights, signs, and point of purchase (POP) overlays.  Fig. V-1 shows a typical UniGlo backlighting  panel.  

The thin profile and flexibility of UniGlo  backlighting panels allows placement between an elastomeric keypad or overlay  and a non-tactile or tactile dome membrane switch. When the elastomeric or overlay is depressed, the UniGlo panel flexes, easily allowing actuation of the switch. Typically, a membrane switch requires 10 to 14 ounces of actuation pressure. UniGlo backlighting panels slightly increase  the snap-through actuation pressure a minor amount as shown in table V-I: 

An independent laboratory conducted  Mechanical/Temperature Life Cycling tests on one-layer and two layer UniGlo  backlighting panels. The panels were  placed between an overlay and a membrane switch and were actuated over five  million cycles at room temperature. Panels were similarly tested for one million cycles at -10† C, and then, one million cycles at -50† C. The panels tested showed no signs of light transmission degradation after any of  these tests. In addition, panels were successfully tested for one million cycles at -55† C.

Table V-I (Force Test Data)

VI.  POLYGLO^® BACKLIGHTING 

Poly-Optical's  patented PolyGlo^® process (U. S. patent numbers 5,097,396, 5,226,105,  5,295,216, and 5,307,245) terminates individual fibers on a POF panel in any  specified pattern (Fig. VI-1).

FIG.  VI-1  (Typical  PolyGlo panel)

The resulting  spots of light may be diffused to create a uniform glow. A diffuser is not  required if the object to be illuminated is diffusive in nature, such as a  translucent elastomeric keypad, or if a decorative effect is desired . 

PolyGlo Select is a process method that selectively terminates fibers in specified areas on a  panel. Panels made by this process are normally used to illuminate the button areas on rubber keypads over a membrane switch set. A typical PolyGlo Select panel is shown in Fig. VI-2.

 FIG. VI-2  (2 x 4 button backlighting panel with  PolyGlo Select)

VII. POLY OPTICAL FIBER  BACKLIGHTING DESIGN FACTORS

This section addresses issues to consider when designing plastic optical fiber backlighting  devices.

Design factors: 

A.  Brightness 
B.  Power budget
C.  Color
D.  Thickness
E.  Assembly
F. Operating environment
G. Human factors

A) Brightness is determined by:

1.  Light source (from LED to halogen and metal halide)
2.  Number of fiber layers
3.  How the fiber layers are  processed
4.  Number of fiber "tails" for  light input
5.  Reflective layers
6.  Brightness Enhancement Film  ("BEF")
7.  Diffusing layer(s)

B)  Power budget is determined by the type of light source

C)  Color is determined by:

1.  Light source selected
2.  Filters between fiber bundle and light source
3.  Filters and inks on the graphic overlay panel

D).  Thickness is determined by the following:

1.  Fiber diameter
2.  Number of fiber layers
3.  Reflective backer
4.  Adhesive layers
5.  Diffuser/brightness enhancement film and filler layers

E)  Assembly:

1.  Thickness
2.  Flexibility
3.  Adhesive layer (top or bottom)
4.  Shape
5.  Transparent area(s)
6.  Optical or electrical  connectors

F)  Operating Environment:

1.  Operating temperature range
2.  Humidity
3.  Ambient light 
4.  Shock and vibration
5.  Dust & particles
6.  Safety
7.  Radiation
8.  Caustic or hostile envirornment

G)  Human Factors:

1.  Brightness
2.  Contrast
3.  Uniformity
4.  Tactility

Design Aids:

If the  product is already being illuminated, a sample of the existing product can be evaluated by Poly-Optical.

In order  for Poly-Optical's application engineers to best address the design factors, it is very helpful that we receive the device to be illuminated, i.e. LCD, membrane switch overlay or elastomeric, graphics, point of purchase overlay.

Design Ideas:

The illustrations in this Section that have the basic elements of plastic optical fiber backlighting are shown in each figure.  They are: 

1.  The light  source
2.  The tail & end-tip
3.  Active illuminated area

Single Ended  Panel

FIG. VII-1  (Typical POF  Panel)

Double Ended  Panel

The active area of a panel lit from both ends is nearly twice as bright as the same panel lit from only one end (See Fig. VII-2).

IX.  PLASTIC LIGHT PIPE ("OptiGlo"®)

Many forms of  light pipes exist. The basic design elements of light pipes are a light source  and a pipe. The pipe typically is some optically clear plastic fiber rod or  sheet.  The design goal of light pipes is  to optically couple a light source™s output into the edge or end of the pipe and  to cause the front surface or distal tip to emit light uniformly. This uniform light output is achieved by  treating any or all of the pipe™s surfaces to achieve the desired effect.  A simple light pipe is shown in Fig. IX-1.

FIG. IX-1  (Typical simple  light pipe)

Light pipes  illuminate due to the treatment of the surface(s). For uniformity, treatments  usually vary in spacing and depth as they are applied farther from the light  source. These devices may be machined or molded into shapes and can be lit from  one or more sides by multiple light sources.

FIG. IX-2 (Light Pipe)

Customers typically elect to use molded plastic panels when a thickness of  1/8 or more is acceptable, production quantity is high, and low unit cost is  required.  A large area light pipe is  shown in Fig. IX-2.

X.  THICKNESS SPECIFICATIONS AND  BRIGHTNESS ENHANCEMENT  FOR  POF BACKLIGHTING  DEVICES

The  thickness of POF backlighting devices is determined primarily by the fiber  diameter and the number of layers. 

Following  is the nominal thickness of UniGlo® and PolyGlo® devices that are made with  .010" diameter fibers with a white reflective film and a layer of adhesive.  (See Fig. X-1)

 Fiber  Device

  Layers  Thickness

1  .013"
2  .025" - .027"
3  .037" - .040"
4  .051" - .053"
5  .064" - .066"
6  .077" - .079"

FIG. X-1

The  brightness of POF backlighting panels is determined by the following  factors:

A.  Type and color of the devices light  source
B.  Number of fiber layers
C.  Number of tails
D.  Reflective layer(s)
E.  Brightness enhancement film
F.  Diffusion layer

Factor  A - Light sources from LEDs to halogen and metal halide lamps provide a wide  range of brightness and color options.

Factor  B - Brightness is increased by adding additional layers of fiber.  The following table indicates an approximate  layer-brightness relationship:

1   1.0 X
2   2.0 X
3   2.6 X
4    3.2 X
5    3.6 X
6    4.4 X

X  is dependent primarily on the brightness of the light source(s) utilized and  whether the panel is illuminated from one or both ends. 

Factor  C - Construction of a backlighting device with "tails"  and light sources on both ends of the panel,  or running both tails into a common light source, results in twice the  brightness of a one tail device.  (See  Fig. X-2)

FIG. X-2

Factor  D - The brightness of a POF panel can be increased by 7% to 15% by adding a  second reflective layer behind the panel or laying the panel on a white  surface. 

(See  Fig. X-3)

FIG. X-3  (Two layer backlighting  panel)

Factor E - Adding a brightness enhancement film (BEF)  significantly increases the brightness measured perpendicular to the surface of  one or two layer POF devices by 50% to 80%.  (See Fig. X-4).

FIG. X-4

(One layer backlighting  panel with brightness enhancement film)

BEF  increases the measured brightness of a POF panel because light leaving a POF  panel exits predominately in the forward direction as it travels from the light  source end to the distal end.  BEF  material has a micro grooved surface that re-directs the emitted light at a more  perpendicular angle from the POF panel.  The same amount of light exits the POF panel but more of the light is  seen when directed into the viewers line of sight and as a result the panel  appears brighter.

Factor  F - Diffusion layers re-distributed light emitted by POF panels to provide  even illumination at all angles.

XI.  LIGHT  SOURCE ENGINEERING GUIDE

Selecting a  light source for a plastic optical fiber application depends on various  requirements such as brightness, fiber bundle size, color, space, power, and  life expectancy.  Poly-Optical's  OptiBeam^® brochure provides technical specifications on numerous  light sources offered by the company. This section provides general guidance  when selecting a light source 

Incandescent Lamps:  When using theselamps, life expectancy, light output,  voltage, and current are all related. A change in voltage cause a mathematically  predictable changes in life, light output, and current.  A slight drop in voltage increases the lamp  life significantly.

The following  formulas can be used to calculate values for life, light output, and current  draw based on changes of voltage for an incandescent lamp. Generally, these  formulas are most accurate when voltage does not increase more than 20% over the  rated voltage. Using a lamp at a voltage that is not the design voltage is  called rerating 

Life Expectancy    LIFE (HRS)   =  (RATED LIFE)

For example, if  a lamp has 1000 hours life, and is rated at 5.0 V, you may operate it at 4.5 V  to increase its life:

  LIFE (HRS)  = (1000 HRS)  =  3541 HRS 

Light output: A common measure of light  is Mean Spherical Candle Power (MSCP), which is the total output of a lamp's  light energy, measured in a sphere.  To  calculate light output from a rated lamp:

OUTPUT  (MSCP) = (RATED OUTPUT)

If a lamp is  rated 10 MSCP at 5.0 V, its total light output at 5.5 V will be:

  OUTPUT  (MSCP)  =  (10  MSCP)  =  14  MSCP

Applied  Current:

CURRENT  (AMPS) = (RATED CURRENT)

If you operate  a 5.0 V, 200 mA lamp at 5.5 V, the load current will be:

CURRENT  (AMPS)  = ( 200 mA) =  211  mA

These formulas  are used for incandescent lamps, not LEDs, halogen or arc lamps. 

Higher voltage  lamps generally have longer or wider filaments.  A long or wide filament can have an adverse effect such as streaks in the  backlighting panel due to filament shadows. It is advantageous to use lower  voltage lamps with thinner/shorter filaments.

Gas and halogen  lamps are considerably brighter than incandescent lamps.

Lamps are often  available with a lensed end to provide increased End Foot Candles (EFC) or  greater brightness at the bulb end.

Light emitting diodes (LEDs) are often  used when lighting plastic optical fiber panels.

T 1 (3 mm  dia.), T 1 3/4 (5mm dia.) LEDs are available in red, yellow, green, white, blue  and multi colors.

LEDs are  popular for backlighting panels due to their  long life, low cost, low power requirements, and low operating temperature.  When a backlit device is viewed in a  low light environment, LEDs are usually the  most cost effective choice. 

LIGHT MEASUREMENTS  AND CONVERSIONS

Power in Light: Optical power like any other physical power is measured in Watt (W), and is  defined as energy per time.

1 W = 1 Joule/  S

Total energy in a ray of light is the sum of energy of all  photons in the ray. Energy carried by each photon follows Planks equation:

E= hc/l

As you can see from the Planks equation, one quantum of  light may have different energy depending on its wavelength. Measurement of  light in broadband of electromagnetic spectrum is called Radiometry . On the other hand, Photometry is measurement of light within the visible region.  Lumen (lm) is the photometric unit of  optical power, weighted to match the human eyes response. Human eye is most  responsive at yellowish-green light of 555 nm in wavelength, so one watt is  highest lumens at this wavelength.

1 watt (@ 555 nm) = 683.0  lumens

Radiant Flux is  total light output from a point source in all directions, which  is measured in watts. Photometric counter  part to radiant flux in photometric unit is called luminous flux and is measured in  lumens. 

Luminous  Intensity:  Luminous flux emitted by  a source in a given range of directions.

The unit of measurement is the lumen/stradian now known as Candela. Direction is measured in unit  of  solid angle, Stradian (sr).  

Lamp and LED output is commonly measured in Candelas and  Lumens. 

When a source propagating uniformly in all directions 

1 Candela (Cd) =  4p lumen (lm) 

Illuminance (visible flux density) is luminous flux incident per unit area of a surface,  and is measured in lumen per square meter or Lux.  Other commonly used units of illuminance are footcandles and phot.

1 Lux = 1  lm/m²

 1 Footcandle  = 1 lm/ft²

  1 Phot = 1  lm/cm²

Luminance (visible flux density per solid angle) indicates brightness of a diffused  surface, and is defined as luminous flux per unit solid angle per unit area  measured normal to the direction of propagation of flux. Some common luminance  units are: footlambert (fL), Stilb (sb), apostilb (asb), and lambert (L).

 1 Lambert =  1/P Cd/cm²

  1  footLambert = 1/P Cd/ft²

  1 Stilb =  Cd/cm²

  1 NIT =  Cd/m²

  1 Apostilb =  1/P Cd/m²

For fiber optic backlighting panels, the units of luminance  measurement used are fL and Nit.

Following are the ftL/Nit relationships.

 One ftL =  3.42 Nits

 One Nit  =   .29

XII.  LIGHT  GUIDES & SCANNERS

Light  Guides 

Light guides  are transparent devices that conduct the flow of  light from a source to the point of  need.  Plastic optical fiber or other  transparent materials can be used as a light guide. 

Type of light  guides are:

A.  Extruded  transparent plastic rods are the simplest type of light guide. 

  (See Fig. XII-1).

B.  A single  plastic optical fiber with cladding results in superior light transmission.  Fig. XII-1.  Fiber diameters are available from .010" to .120".  (See Section XVI).

C.  A bundle of plastic optical  fiber results in a larger diameter flexible light guide.  The bundle can be split into two or more legs  to illuminate multiple locations with a single light source.  Standard bundle diameters are 1/16", 1/8",  1/4" and 1/2" in 2, 4 and 6 foot lengths.  Custom sizes and configurations are available.

D.  Large core light guides are made  in diameters up to .700".  They consist  of a teflon tube (the cladding) and a soft flexible polymer core.  The advantage of a large core light guide  over a fiber bundle is that there is no loss due to space between the  fibers.  See Section XV.  The advantage of the bundled fibers is that  they are more flexible and have lower loss per unit  length. 

Scanners

POF scanners  are optical devices which have a bundle of fiber at one end and a flat array of  fiber at the other end (called "OptiLine" devices by Poly-Optical).  The devices are used as scanners or for front  splash lighting.  Fig.  XII-2.

OptiLine  devices can have multiple fiber layers and can have bifurcated tails to result  in different colors of light per layer and or on/off capabilities for different  sections of the device.

XIII.  IMAGING LIGHT  GUIDES

1.  Construction

Image guides  are a special type of light guide made by bundling many (a few to  thousands)  very small fibers in such a  manner that the fibers maintain their relative position in the bundle from end  to end. With this coherent arrangement, an image projected onto one end of the  bundle will be reproduced on the other end. The smaller the diameter of each  fiber the better the resolution of the image.

2. Application

Image guides  are used in medical and industrial applications for viewing objects in remote or  difficult to access locations. Quite often there is no light in these locations  and it is necessary to provide illumination with the use of a second light guide  as shown in Fig. XIII-1.

FIG. XIII-1  (Typical image guide with  associated light guides)

XIV.  SCINTILLATING & FLUORESCING FIBERS  ("OptiBright"®)

1. Construction

Plastic optical fibers can be doped with a florescent  material that absorbs light at short wavelengths, typically in the ultraviolet  and blue (370nm to 550nm wavelengths) and then re-emits the energy in longer  wavelengths. The material can be chosen to re-emit the light in red, green,  yellow and blue wavelengths. A portion of the light that is re-emitted from the  florescent material is trapped in the fiber and is guided to the ends. As the  fiber is made longer the amount of light trapped in the material accumulates and  causes the light emitted from the end of the fiber to increase in intensity. As  the intensity of the ambient light increases the intensity of the light at the  end of the fiber increases so the fibers are very effective in bright  environments.

The material can be made in  sheets and injection molded so that irregular shapes can be fabricated. In the  sheet form the light is guided to the edges, which gives the edge a bright  appearance.

2. Applications

These devices can be used in decorative applications,  indicators, signs and where it is desirable to attract attention to a specific  point.

XV.  SPARKLEGLO

SparkleGlo is side-lighting  plastic optical fiber, abraded on four sides.  SparkleGlo is available in .060,  .080,.100 and .120 nominal diameters.  A sparkling line of light is created  when this fiber is lit from both ends.  For shorter lengths, lighting from one  end may be satisfactory.  Best results are achieved when SparkleGlo devices are  not longer than ten feet.  Photo shows SparkleGlo lit from both ends with green  LEDs. 

SparkleGlo may be used for  decorative applications.  LEDs may be powered by one or more batteries, and LEDs  may flash on and off for longer life.

XVI.  LUMIGLO LARGE CORE OPTICS

LumiGlo is a solid core, Teflon clad, flexible,  large core optic.  Side-light optics and  polyethelene jacketed end-light optics are offered in diameters ranging from  1/4 to 3/4.

TECHNICAL DATA

Attenuation:  approx. 2% per foot
Operation temperature:  -40† C to 120† C
Bend radius minimum:  6 times diameter
Cone angle:  82† nominal
Numerical aperture:  0.66

Associated  Hardware

Light Sources
Color Wheels
Tracking Hardware
Clips and End Seals
Fiber Cutters
Harnesses for Multiple Light  Cables
Splice Kits
LumiGlo large core optic with  OptiBeamâ
RB1100 light source 

XVII.  LUMILEEN OPTICAL FIBER

Lumileen is Poly-Optical™  trademark for its line of plastic optical fibers.

typical Lumileen plastic optical fiber (POF)  consists of an inner acrylic plastic core coated with a thin cladding of  fluorinated polymer.  Since the  refractive index of the outer cladding is lower than the core, light entering  one end of a fiber reflects along the interior core material at the interface of  the core and cladding.  Light passes  through the length of the fiber in a zigzag path on its way to the other  end.  (See the figure  below).

Transmission  loss of Industrial and Optical Grade Lumileen Optical  Fibers

Transmission loss of attenuation  increases below 400nm and above 800nm. However, satisfactory results can be  achieved in these extreme ranges. As a general rule, light is still detectable  in plastic optical fiber after propagation of over 100  feet.