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How to choose a tunable laser?

Tunable lasers offer great flexibility to researchers and also industrials. They are used in many different applications areas: atmospheric sensing, biomedicine, microscopy, spectroscopy, atom cooling, defense, medicine, and more. We cannot help but notice that there is more than one type of tunable laser available on the market. What are the differences between those lasers? How to make a choice between them? Here is a quick summary of the tunable lasers available today and their range of performances. Something missing? Some…

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What makes my laser mode hop?

Mode hops are often provoked by external influences as laser case temperature, length drifts of the laser resonator, injection current and optical feedback. And as a matter of fact, mode hops often result from attempts to tune the wavelength of a laser. Let’s see here the two main causes behind laser mode hopping: temperature and injection current. Temperature The laser cavity can support many different wavelengths or longitudinal modes. In laser diodes, these modes are separated by typically 10 to…

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Why does my laser mode hop?

Mode hopping is characterized by a stochastic exchange of power between two longitudinal modes of a laser, inducing a high-level intensity noise in the laser’s output. You can read more about why is laser mode hopping so bad for many applications in a previous article. We will review here why laser mode hopping occurs in semiconductor lasers. The mode wavelengths and the gain peak wavelength depend on the laser’s temperature: the mode wavelengths shift with temperature at about typically 0.06 nm/°C, while…

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Why is laser mode hopping so bad?

Semiconductor lasers have found widespread use in fiberoptic communications, entertainment (videodisc and compact disc players), merchandising (bar-code scanners), and in the scientific field as well (spectroscopy) thanks to their variety of wavelengths, compact size, low price and ease of control. Unfortunately some applications require a minimum degree of stability of wavelength that is not always met by semiconductor lasers, especially when mode hopping occurs. Before reviewing why laser mode hopping is so bad, let’s remember what mode hopping refers to….

Strainmeter to detect earth tide and seismic waves from earthquakes

Strainmeter based on laser wavelength monitoring

We have seen in a previous article that a set-up based on a laser and Optical Fiber Bragg grating (FBG) sensors can be used for strain and temperature monitoring. This technique is based on the monitoring of reflected laser wavelength. FBG sensors find one application in seismology. Strain monitoring is well known in the field of seismology for earth science observation purposes. Strainmeters measure deformation over periods of days, months, and years. This allows them to measure signals at lower…

Monitoring a laser wavelength for strain and temperature

How a laser enables you to monitor temperature and strain variations?

Lasers are also used in set-ups aimed for monitoring strain and temperature. In those set-ups strain and temperature variations are directly proportional to the shift of a reflected laser wavelength. Optical Fiber Bragg Gratings (FBG) are known for many years and allow using an optical fiber as a Temperature + Strain + Pressure sensor. An optical fiber Bragg grating acts as a mirror at a specific wavelength depending on the distance between its lines, and transmits all others, or acts…