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NTC Thermistor Chip Application in Optical Communication
2018/03/28 05:03:06

NTC Thermistor Chip Application in Optical Communication

Modern society has entered the information age, the need for prompt and timely information is urgent, so the speed and efficiency of communication requirements are getting higher and higher, optical communication just to meet this requirement.

In the field of optical communication, Electlro-absorption Modulated Laser (EML) is used for high speed, long distance communication requires high temperature stability and is moving towards miniaturization and high density. EML lasers are the first mass-produced indium gallium arsenic phosphorus (InGaAsP) optoelectronic integrated devices. It is an integrated laser source and an electroabsorption external modulator on the same semiconductor chip. It has the advantages of low driving voltage, low power consumption, high modulation bandwidth, small size and compact structure. It is more suitable for high speed and long distance than traditional DFB lasers.

The output wavelength, current threshold, maximum output power and minimum power fluctuation of the EML laser are directly affected by the operating temperature. At the same time, the chirp of the light source is limited by the maximum allowable dispersion of the optical channel. Although the fiber amplifier can extend the signal transmission distance, the linearity of the dispersion value with the transmission distance is independent of the fiber amplifier, so only the chirp of the light source harsh demands. The use of direct modulation lasers far can not meet the requirements of the system for light source performance. As for current technology, the simplest method is to use a thermally controlled laser source with temperature control.

Thermo Electric Cooler (TEC), which is small size and easy to control, is used as a cooling and heating device, and a high-precision negative temperature coefficient thermistor (NTC) is used as the temperature sensor. The MCU is used as the control core and the EML laser Precise temperature control.

At present, most EML lasers are integrated with TEC and thermistor inside. According to CyOptics 10 Gb /s Cooled EML manual, we can see that the operating temperature range of the laser is -40 ~ 90 ℃, TEC thermoelectric cooler current ITEC is -1.5 ~ 1.5 A, VTEC -3.3 ~ 3.3 V, thermistor current ITHC should not exceed 100μA, the range of central wavelength is 1530 ~ 1565 nm, and the wavelength deviation of the temperature of each change 1 ℃ is should not exceed 0.13 nm.

Combined with the specific indicators of the laser, achieve the precise control of the TEC temperature can be divided into the following three steps:

①NTC thermistor real-time monitoring temperature;
②TEC on the current direction to achieve cooling and heating;
③ PID accurately, quickly and steadily control the TEC current.

EML internal integrated high sensitivity NTlC thermistor, the temperature characteristics of small fluctuations in response to a variety of temperature changes, the material is generally thin film platinum resistance. The relationship between the resistance and the temperature of the resistor is non-linear. 

It can be expressed as: R = RTO × EXP {B (1 / T-1 / TO)} among T0 is the initial value of temperature and B is the thermal index.

NTC thermistor as a sensor to detect the internal temperature of the laser, and the temperature is converted to their own resistance changes, and then by the temperature control circuit will change the resistance of the voltage changes, the conversion accuracy determines the accuracy of temperature measurement. The magnitude of the converted voltage determines the flow (inflow or outflow) of the current of the TEC circuit to achieve the cooling or heating of the TEC control circuit.

In summary, the optical communications industry to ensure high speed and effective information transmission needs a stable laser transmission, and the current technology are mainly depend on temperature control settings, temperature control can not be separated from the NTC thermistor. So for my company's products is also a development opportunity. Both the gold electrode and the silver electrode thermal chip have a suitable market. Gold electrode products more stable, but the price is higher. The advantage of silver electrodes lies in cost. Division I according to different customer needs to produce the corresponding products.

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