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Precautions for Use of TOSLINK

(1) Reliability

In an optical module that has been in use for some time, nearly all of the deterioration in characteristics is due to a reduction in

the fiber-output power (Pf). This is due to deterioration over time in the level of optical output of the LED used as the light source.

The drop in the LED's optical output is thought to be caused by crystal flaws in the wafer or stress in the mold resin, although

the detailed causes are not clear.

Although LEDs used for optical communications are generally considered to have an almost infinite lifetime, their optical output

does fall over time.

The life of light-emitting devices is greatly affected by the operating conditions and operating environment as well as by the

lifespan characteristics of the particular device.Toshiba recommends that the user first check a device's lifetime characteristics

before selecting it and setting its operating conditions.

For information on reliability, contact a Toshiba sales office. Regular maintenance, such as a check on the amount of light

emitted is recommended.

In the case of the red LEDs used in the TOTX195 and TODX297, for example, a light-absorbing layer may form on the surface

of the LED as the aluminum in the liquid crystal oxidizes, causing the optical output to fall. Since this tendency is pronounced in

high-humidity environments, it is recommended that products containing red LEDs not be used in such environments. For high-

humidity environments or applications requiring a long lifespan, Toshiba recommends a TOSLINK ceramic-package optical

module.

(2) Soldering

Optical modules use semiconductor devices but are essentially optical components. When soldering, ensure that flux does not

adhere to the light-emitting or light-receiving surfaces.

Take the same care when cleaning off flux after soldering.

Some optical modules include a protective cap. This cap is intended to prevent accidental operation when the module is not in

use. It is not dust- or waterproof. Because the optical module is an optical component, Toshiba does not recommends soldering

methods or post-solder flux cleaning methods in case where flux could affect the module. Toshiba recommends first soldering

without mounting the module, then cleaning the PCB. The module should then be hand-soldered and no subsequent cleaning

should be performed.

If it is not possible to hand-solder the module, one way of avoiding the effect sof flux is to use non-halogen (chlorine-free) flux,

taking care not to leave chlorine or other residue, and omitting the post-solder cleaning. In such cases too, the reliability of the

device must be checked. Be sure to check the reliability of the device.

(3) Noise Resistance

The case for the TOSLINK (simplex) optical receiving module and (duplex) optical transceiver module is made of

conductive plastic.

The case is designed to provide shielding when the reinforced pin at the front of the module is grounded. When the module is

used, this pin should be connected SIGNAL-GND.

Since the case for the optical receiving module and optical transceiver module has a resistance of several tens of ohms,

ensure that the case does not touch the power line or any other circuits.

Generally, the use of optical transmission devices is considered to improve noise resistance.

While optical fibers are certainly not affected by noise, optical modules, particularly receiver modules, are comparatively easily

affected by noise because they handle such minute current signals.

To improve noise resistance, the TOSLINK case is treated to make it conductive. However, since the signal output from the

optical receiving modules photodiode is a minute current signal, in some environments simply shielding the case will not

protect against noise. When using a TOSLINK device, conduct live tests to check noise resistance.

A simple noise filter is mandatory for the power lines for the TOSLINK optical receiving module and optical transceiver module.

However, in the case of significant power supply ripples, further filter reinforcement is also necessary. In addition, when the

optical module is placed in a location susceptible to emission noise, Toshiba recommends covering the optical module and

power supply filter with a metal cover to enhance the shielding.

(4) Protective Cap

When the optical module is not in use, cover it with the protective cap.

Take particular care with the optical receiving module since, depending on the circuit used, extraneous light may be input to the

module when the TOSLINK device is not in use and may adversely affect other circuits.

(5) Vibration, Shock and Stress

Plastic-molded optical modules are plastic-sealed devices whose wires are fixed with resin. While this structure makes them

comparatively resistant to vibration and shock, wire breakage has been observed in equipment in which the module is used

when the soldering and connections are exposed to vibration, shock or stress. Therefore, when using a plastic-molded optical

module in equipment with high vibration levels, ensure that the structure is designed to withstand vibration, shock and stress.

Ceramic-package optical modules are ceramic-sealed, with a hollow interior. Since the wires in the module are not fixed, the

module is susceptible to vibration and shock.

Therefore, when using a ceramic-package optical module in equipment which is subject to high levels of vibration and shock,

ensure that the structure of the equipment is designed to withstand vibration, shock and stress.