ApplicationNote
senko.com

Laser Eye Safety
for Telecommunications Systems
FEBRUARY 2019Rev. 01

Issued by:EngineeringDepartment

Created by:
Dr. Bernard Lee
Eric Staley
Larry Johnson

www.senko.com

Application Note

Laser Eye Safety
for Telecommunications Systems
Introduction

aided by focusing from the lens of an eye, can cause laser radiation to be concentrated into an extremely
small spot on the retina. A transient increase of only 10 °C can destroy retinal photoreceptor cells. If the laser iseyeball and may cause heating of the retina, whereas exposure to laser radiation with wavelengths less than
400 nm and greater than 1400 nm are largely absorbed by the cornea and lens, leading to the developmentof cataracts or burn injuries.
RetinaIris

MaculaCornea

Optic nerve
Pupil
Vitreous

1Lens

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Infrared lasers are particularly hazardous, since the body’s protective “blink reflex” response is triggered only byvisible light. For example, some people exposed to high power Nd:YAG laser emitting invisible 1064 nm radiation,
may not feel pain or notice immediate damage to their eyesight. A pop or click noise emanating from the eyeball
may be the only indication that retinal damage has occurred i.e. the retina was heated to over 100 °C resulting in
localized explosive boiling accompanied by the immediate creation of a permanent blind spot.

Ocular Absorption Site vs. Wavelength

Visible and Near-infared(400 - 1400nm) radiation

Mid-infared and Far-infared(1400 - 1mm) andFar-ultraviolet(180nm - 315nm) radiation

Near-ultraviolet(315 - 390nm) radiation

Lasers can cause damage in biological tissues, both to the eye and to the skin, due to several mechanisms.
Thermal damage, or burn, occurs when tissues are heated to the point where denaturation of proteins occurs.
Another mechanism is photochemical damage, where light triggers chemical reactions in tissue. Photochemical
damage occurs mostly with short-wavelength (blue and ultra-violet) light and can be accumulated overthe course of hours. Laser pulses shorter than about 1 μs can cause a rapid rise in temperature, resulting in
explosive boiling of water. The shock wave from the explosion can subsequently cause damage relatively faraway from the point of impact. Ultrashort pulses can also exhibit self-focusing in the transparent parts of theeye, leading to an increase of the damage potential compared to longer pulses with the same energy. Theeye focuses visible and near-infrared light onto the retina. A laser beam can be focused to an intensity on theretina which may be up to 200,000 times higher than at the point where the laser beam enters the eye. Mostof the light is absorbed by melanin pigments in the pigment epithelium just behind the photoreceptors andcauses burns in the retina. Ultraviolet light with wavelengths shorter than 400 nm tends to be absorbed bylens and 300 nm in the cornea, where it can produce injuries at relatively low powers due to photochemical
damage. Infrared light mainly causes thermal damage to the retina at near-infrared wavelengths and to more
frontal parts of the eye at longer wavelengths. The table below summarizes the various medical conditions
caused by lasers at different wavelengths, not including injuries due to pulsed lasers.
Wavelength Range

2

Pathological Effect180–315 nm (UV-B, UV-C)

photokeratitis (inflammation of the cornea, equivalent to sunburn)

315–400 nm (UV-A)

photochemical cataract (clouding of the eye lens)

400–780 nm (visible)

photochemical damage to the retina, retinal burn780–1400 nm (near-IR)

cataract, retinal burn1.4–3.0μm (IR)aqueous flare (protein in the aqueous humour), cataract, corneal burn

3.0 μm–1 mm

corneal burn

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Fibre Optic Safety Standards
The evolution of fiber optic components, systems andtechnology to address data rates in the gigabits requires
the use of laser diodes in most applications due to speed
requirements. Even short distance multimode systems, whichin the past used LEDs, have now migrated to low cost VerticalCavity Surface Emitting Laser sources (VCSEL). For this reason,
all fiber systems must be treated as if they are carrying a laser
signal. Attention on how to address Laser safety and thesafe design, use, and implementation of lasers is required tominimize the risk of eye accidents. Laser classifications arebased on the concept of accessible emission limits, or AEL.
This is usually a maximum power level in watts, or energy
level in joules that can be emitted at a specific wavelengthand exposure time.
In the United States, lasers are regulated by the Center
for Devices and Radiological Health, or CDRH. A branchof the FDA. the CDRH is responsible for overseeing themanufacturing, importation, performance, and safety of all
medical devices as well as devices that emit certain types ofelectromagnetic radiation, including lasers. With lasers, theCDRH is concerned that the devices are properly labeled as
to their output power and are equipped with the appropriate
safety equipment if necessary.
A number of organizations have developed standards andguidelines for safely working with optical fiber, cables, andoptical transmission equipment. These include the ANSI
Z136.2 American National Standard for the Safe use of
Optical Fiber Communication Systems Utilizing Laser Diodeand LED Sources and also the OSHA standard on laser safety
STD-01-05-001. For international use, the IEC 60825-1 covers
the safety of laser products, and the IEC 60825-2 covers thesafety of optical fiber communications systems (OFCS).
The ANSI Z136.2 and the IEC 60825-2 standards divide laser
devices into a set of 4 general classes and several sub-classes
based on their wavelength and optical power output. The
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first version of the standard was published in 1988 at a time when laser-based fiber optic communications systems
were very simple. They used only two wavelengths, 1310 and 1550 nanometers, at maximum power levels wellunder 10 milliwatts. The standard was the first written specifically for fiber optic communications systems.
Under the ANZI 136.2 standard, an end-to-end fiber optic system is considered a Class 1 laser product because
under normal conditions the laser emissions are completely enclosed. It is not until the fiber is broken or aconnector is unplugged that a person may be exposed to laser radiation which may be potentially hazardous.
Therefore, the hazard level for each optical port must be individually assessed, and control measures defined. To
address such situations, the standard defines the hazard level as the potential optical hazard at any accessible
location within a fiber system, depending on the level of the radiant energy that could become accessible.
Hazard levels are assigned values from 1 to 4 based on the customary laser accessible emission limits, or AELs.

Personal Protective Equipment

Laser Safety Eyewear Courtesy Laservision USA
To safely work with optical fibers, a wide variety of personal protective equipment and other safety tools
will be needed. All personnel must conform to federal, state and local laws requiring personal protection
equipment to be worn while performing specific operations. This equipment includes specialty eyewear for
use with lasers. Protective eyewear in the form of glasses or goggles with appropriate filters can protect theeyes from direct or reflected laser light. If the optical power is high enough, the use of goggles, which provide
better protection from the sides, are a better choice.
Eyewear must be selected for the specific type of laser, to block or attenuate in the appropriate wavelength
range. Laser protective eyewear is rated for optical density, or OD, which is the base-10 logarithm of theattenuation factor by which the optical filter reduces beam power. For example, eyewear rated as OD 3 will
reduce the beam power at the specified wavelength range by a factor of 1,000.
OD

4Attenuation

Transmission

1

100.1

2

100

0.01

31,0000.001

410,0000.00015
6100,000
1,000,000

0.00001
0.000001

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In addition to an optical density sufficient to reduce beam power to below the maximum permissible exposure,laser eyewear used where direct exposure is possible should be able to withstand a direct hit from the laser
beam for at least 10 seconds without breaking. The wavelengths and optical densities are usually printed on
the glasses or goggles, often near the top. This safety eyewear differs from that used with lasers because it is notconcerned with attenuating light, but rather keeping foreign objects and particles from entering the eyes.

Safety Features in Modern Optical Components
Protection to those working on energized fibers and patching solutions is an important consideration in
the design of today’s fiber optic components and systems. System designers are more often calling out for
devices that offer some level of protection beyond the standard warning labels and safety handling guidelines.
Uncapped fiber ports can be commonplace in networks as adapter dust caps regularly go missing once a
connector is installed and then a change is required and the patch cable is moved.
To address these issues, component manufacturers have installed shutters internally on some fiber optic
mating adapters. Early generation product provided eye safety, yet dust ingress protection remained an issue
and contact between the ferrule end face and the shutter was an issue in some designs. Recent advancements
have solved this issue through improved shutter design that prevents dust from entering the critical area ofan adapter when unmated and allow for insertion of the connector without any contact between the shutter
and the connector ferrule.

SENKO’s Shuttered MPO and LC Adapters
As a compliment to the shuttered adapters, some connector designs are implementing an integral shutter foradditional protection. The E-2000™ and SC APC connectors are examples of two currently available solutions.

BEFOREM AT I N G

E-2000™

A F T E R
M AT I N G

Shutter

SC APC Shuttered Connector
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Biography
Bernard is a senior telecommunications andbusiness strategy professional with more than 15
years of global experience in telecommunication& data communications arena especially in

Bernard Lee

is currently the Regional Technology Director
at SENKO Advanced Components Bernard isan Expert at the International ElectrotechnicalCommission (IEC), a Chartered Engineer (CEng)
accredited by the Engineering Council of UK,
a Professional Engineer (PEng) registered withthe Board of Engineers Malaysia and also aBICSI Registered Communications Distribution
Designer (RCDD). In the past 15 years, Bernard has
designed, commission and audited numerous
communications networks.
Eric is a Product Manager at SENKO Advanced
Components and has been with the company
since 2007. Prior to joining SENKO, he wasinvolved in Sales with a major cable assembly
manufacturer, a national distributor of electricaland communication products and has over 20

Eric Staley

Larry Johnson started his career in the early days
for Tektronix he was involved with the earlytest & measurement standards for the TIA and ANSI
including the ANSI Z.136.2 “Safe Use of Optical Fiber
Communication Systems Utilizing Laser Diodesand LED Sources” standard. In 1986 he founded
The Light Brigade and researched and wrote overLarry Johnson

Larry provides expertise through FiberStory he isalso a member of multiple industry technology
committees including the Utility Telecom Council(UTC) and the Fiber Broadband Association(FBA). For the Optical Fiber Conference (OFC)
coordinated by the Optical Society of America(OSA) he has provided many specialty courses
special events including the FTTH and Test &Measurement centers and also moderates panels
on various topics. In 2018 he wrote the chapter on“Fiber Optic Safety in Telecommunications” for CRC
Press’s “Understanding Laser Accidents” book. He is
also the Fiber Optic Columnist writing a monthly
service providers.
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