Laser diodes of DWD-RW drives can cut and burn! A simple circuit drives the laser diode and controls the output power Connect an an 40 dual frequency laser diode

Writers DVD drive ov, despite the total dominance of flash drives, there are still a lot left. Many of them are lying around, not working - it’s a shame to throw them away, but it’s unclear where to use them... Well, at least make a homemade 1-watt laser, with which you can light matches no worse than using expensive ones from Aliexpress. But you can’t just connect a laser diode to a battery - you need a driver (a correct voltage generator).

Laser power driver circuit

A voltage-controlled current source circuit can be used to control the constant flow of current through a laser diode. This simple linear driver provides cleaner power to the laser diode than classic PWM (PWM).

Device settings

• Element power supply - 3.3 V direct current
• Load current up to 300 mA (when changing the circuit to 1 A)
• Smooth adjustment of laser power using a variable

The laser diode current results in a differentially measured voltage drop across a shunt resistor (RSHUNT) in series with the laser diode. The flow of the output is controlled by the voltage input (VIN) which comes from the Pr1 regulator balancing it.

If necessary, the output current can be increased several times by changing the transistor to a more powerful one (providing a heat sink) and lowering the resistance of the shunt resistor. You can download the board drawing.

We warn you: if you burn out your eyes through your stupidity, it’s not our fault!

When generating laser radiation, it is not the laser diode current that is more important, but its voltage. At the moment a positive potential is applied to the anode, a displacement begins p-n junction in a straight direction. This begins the injection of holes from the p-band into the n and a similar injection of electrons in the opposite direction. The close proximity of electrons and holes triggers their recombination. This action accompanied by the generation of photons of a certain wavelength

This physical phenomenon is called spontaneous emission and, as applied to laser diodes, is considered the main method of generating laser radiation.

The semiconductor crystal of a laser diode is a thin rectangular plate. The division into p and n parts here is carried out according to the principle not from left to right, but from top to bottom. That is, at the top of the crystal there is a p-region, and below there is an n-region.

That's why area p-n transition is large enough. The end sides of the laser diode are polished, since to form an optical resonator (Fabry-Perot) it is necessary to have parallel planes of maximum smoothness. A photon directed perpendicularly to one of them will move along the entire optical waveguide, periodically reflecting from the side ends until it leaves the resonator.

During such movement, the photon will provoke several acts of forced recombination, i.e. the generation of similar photons and thereby enhancing the laser radiation. At the moment in time when the gain is sufficient to cover the losses, lasing begins.

home distinctive feature between LEDs and laser diodes is the width of the emission spectrum. LEDs have a wide spectrum of radiation, while lasers have a very narrow spectrum.

The operating principle of both semiconductor sources is based on the phenomenon of electroluminescence - the emission of light by the material through which it flows. electricity induced by an electric field. Emission due to electroluminescence is characterized by a relatively narrow spectrum with a width of 0.1...3 nm for laser diodes and 10...50 nm for LEDs.

To connect a laser diode, you need a special electronic circuit, called a laser diode driver. On practical example Below we will show you how to assemble a simple laser diode driver based on the LM317 voltage regulator with your own hands.

The driver is a special connection circuit that is used to limit the current and then supply it to the laser diode so that it works correctly and does not burn out the first time it is turned on, if we directly connect it to the power supply.

If the current is low laser led will not turn on due to lack of the required power level. Thus, the driver circuit is designed to provide the correct current rating at which the laser diode will enter its operating state. For a simple LED, a regular resistor will suffice to limit the current, but in the case of a laser, we will need a connection circuit to limit and regulate the current. Microassembly is perfect for these purposes.

The three-pin LM317 microcircuit is a typical voltage stabilizer. At its output it can produce voltage from 1.25 to 37 volts. Appearance The LM317 with labeled pins is shown in the image above.

The microcircuit is an excellent adjustable stabilizer, in other words, you can easily change the output voltage value depending on the needs of the circuit output, using two external resistances connected to the Adjust line. These two resistors act as a voltage divider used to reduce the output voltage level.

The design can be assembled on a breadboard in five minutes. The scheme works like this. When a voltage of 9 volts begins to flow from the battery, it first flows through a ceramic capacitor (0.1 µF). This capacitance is used to filter high frequency noise from the DC source and provides the input signal to the stabilizer. A potentiometer (10KΩ) and resistors (330Ω) connected to the tuning line are used as a voltage limiting circuit. The output voltage depends entirely on the value of these resistances. The output voltage of the stabilizer goes to the filter of the second capacitor. This capacitance acts as a power balancer in filtering out fluctuating signals. As a result, you can change the intensity of the laser radiation by rotating the potentiometer knob.

The invention of the semiconductor laser diode is deservedly considered one of the best achievements in the field of physics of the second half of the last century. Independent developments by Soviet and American scientists in the field of optical radiation of solid-state materials, carried out more than half a century ago, today show their effectiveness in the domestic, industrial and military spheres.
Unlike light-emitting diodes, whose operation is based on the spontaneous emission of photons, laser diodes have a more complex operating principle and crystal structure.

Principle of operation

To understand where photons come from, consider the process of recombination (the disappearance of a pair of free carriers - an electron and a hole). When direct voltage is applied to the p-n junction of the diode, injection occurs, i.e. a sharp increase in the concentration of nonequilibrium carriers. During the injection process, electrons and holes moving towards each other recombine, releasing energy in the form of a particle - a photon and a quasiparticle - a phonon. This is how the spontaneous emission observed in LEDs occurs.

In the case of a laser diode, instead of a spontaneous one, it is necessary to launch the mechanism of stimulated emission of photons with the same parameters. To do this, an optical resonator is formed from the crystal, passing through which a photon with a given frequency forces the electronic carriers to recombine, which contributes to the emergence of new photons of the same polarization and phase. They are called coherent.

In this case, laser generation is possible only if there is excessive large quantity electronic media at the upper energy level, released as a result of injection. To do this, use a pump current of such strength as to cause an inversion of the electron populations. This phenomenon means a state in which top level much more populated with electrons than the lower one. As a result, the emission of coherent photons is stimulated.

Further, such photons are repeatedly reflected from the edges of the optical resonator, triggering the launch of positive feedback. This phenomenon is of an avalanche-like nature, as a result of which a laser beam is born. Thus, the creation of any optical generator, including a laser diode, requires the fulfillment of two conditions:

• presence of coherent photons;
• organization of positive optical feedback (POF).

To prevent the formed beam from scattering due to diffraction, the device is equipped with a collecting lens. The type of lens installed depends on the type of laser.

Types of laser diodes

Over the years of development, the laser diode device has undergone many changes. Its design has been improved, largely thanks to the advent of high-tech equipment. The highest precision of doping and polishing of the semiconductor crystal, as well as the creation of a heterostructural model, are the factors that ensured a high reflection coefficient at the crystal-air interface and the formation of coherent radiation.

The first laser diode (diode with a homostructure) had one p-n junction and could operate exclusively in pulsed mode due to the rapid overheating of the crystal. It has only historical significance and is not used in practice.

A laser diode with a double heterostructure (DHS diode) turned out to be more efficient. Its crystal is based on two heterostructures. Each heterostructure is a material (gallium arsenide and aluminum gallium arsenide) with a low bandgap, which is located between layers with a larger bandgap. The advantage of a GVD laser diode is a significant increase in the concentration of oppositely polar carriers in a thin layer, which significantly accelerates the manifestation of positive feedback. In addition, the reflection of photons from heterojunctions leads to a decrease in their concentration in the low gain region, and therefore increases the efficiency of the entire device.

A quantum well laser diode is designed on the principle of a GVD diode, but with a thinner active region. This means that elementary particles, falling into such a potential well, begin to move in the same plane. The quantization effect in this case replaces the potential barrier and serves as a radiation generator.

The insufficient efficiency of light flux confinement in DGS diodes led to the creation of a heterostructure laser with separate confinement. In this model, the crystal is additionally covered with a layer of material on each side. Despite the lower refractive index of these layers, they confidently retain particles, acting as a light guide. SCH technology occupies a leading position in the production of diode lasers.

Distributed feedback (DFB) laser diode is a part of optical equipment in the field of telecommunications systems. The wavelength of the DFB laser is constant, which is achieved by applying a transverse notch to the semiconductor in the region of the pn junction. The notch performs the function of a diffraction grating, thereby returning photons with only one (specified) wavelength to the resonator. These coherent photons are involved in amplification.

A surface-emitting laser diode with a vertical resonator or a vertically emitting laser VCSEL, unlike the previously discussed devices, emits a beam of light perpendicular to the surface of the crystal. The VCSEL design is based on the method of using vertical optical microcavities with mirrors, as well as achieving the GVD and quantum well techniques. The advantage of VCSEL technology is temperature and radiation stability, the possibility of group production of crystals and their testing directly at the manufacturing stage.

A modification of the VCSEL is a VCSEL with an external resonator (VECSEL). Both laser diodes are positioned as high-speed devices with the ability to provide future data transmission at speeds of up to 25 Gbit/s via fiber optic communications.

Types of cases

The popularization of laser diodes forced manufacturers to independently develop new types of packages. Taking into account their specific purpose, companies produced more and more new types of protection and cooling of the crystal, which led to a lack of unification. Currently, there are no international standards governing laser diode packages.
Trying to restore order, large manufacturers enter into an agreement among themselves on the unification of buildings. However, before practical use of an unknown laser diode, you should always clarify the purpose of the pins and the wavelength of the radiation, regardless of the familiar type of package. Among commercially produced semiconductor lasers, the most common are two types with the following packages.
1 Devices with an open optical channel:

• TO-can (transistor-out-line metal-can package). The housing is made of metal and is used in the manufacture of transistors;
• C-mount;
• D-mount.

2 Devices with fiber output:

• DIL (Dual-In-Line);
• DBUT (Dual-Butterfly);
• SBUT (Single-Butterfly).

Application

Each type of laser diode has practical applications due to its unique features. The cost of low-power samples has decreased significantly, as evidenced by their use in children's toys and pointers. They are equipped with laser rangefinder tape measures, which allows one person to measure distances and related calculations. Red lasers are used to operate barcode readers, computer keypads and DVD players. Some types are used in scientific research and for pumping other lasers. Laser diodes are most in demand for data transmission in fiber optic networks. New VCSEL models offer speeds of 10 Gbps, opening up additional features for a range of telecommunications services, including:

• contribute to increasing Internet speed;
• improving telephone and video communications;
• improve the quality of television reception.

The improvement of the laser diode has resulted in an increased service life, which is now comparable to the mean time between failures of light-emitting diodes. Reducing the pump current increased the reliability of the devices, and their contribution to the development of technical progress is no less than that of other electronic components.

Each of us held in our hands laser pointer. Despite the decorative use, it contains a real laser, assembled on the basis of a semiconductor diode. The same elements are installed on laser levels and.

The next popular product assembled on a semiconductor is your computer's DVD burner drive. It contains a more powerful laser diode with thermal destructive power.

This allows you to burn a layer of the disc, depositing tracks with digital information on it.

How does a semiconductor laser work?

Devices of this type are inexpensive to produce and the design is quite widespread. The principle of laser (semiconductor) diodes is based on the use of a classic p-n junction. This transition works the same as in conventional LEDs.

The difference is in the organization of radiation: LEDs emit “spontaneously”, while laser diodes emit “forced”.

The general principle of the formation of the so-called “population” of quantum radiation is fulfilled without mirrors. The edges of the crystal are mechanically chipped, providing a refractive effect at the ends, akin to a mirror surface.

For getting various types radiation, a “homojunction” can be used, when both semiconductors are the same, or a “heterojunction”, with different materials transition.


The laser diode itself is an accessible radio component. You can buy it in stores that sell radio components, or you can extract it from an old one. DVD-R drive(DVD-RW).

Important! Even the simple laser used in light pointers can cause serious damage to the retina of the eye.

More powerful installations, with a burning beam, can deprive vision or cause burns to the skin. Therefore, use extreme caution when working with such devices.

With such a diode at your disposal, you can easily make a powerful laser with your own hands. In fact, the product may be completely free, or it will cost you a ridiculous amount of money.

DIY laser from a DVD drive

First, you need to get the drive itself. It can be removed from an old computer or purchased at a flea market for a nominal cost.

This scheme is quite accurate and does not require large number components, is designed to control a laser diode and is designed in accordance with the requirements for medical equipment. The device is currently undergoing clinical trials. The performance of laser diodes is subject to short- and long-term drift due to temperature and aging. They are usually driven by direct current, so their optical output power is monitored and the current is adjusted according to changes in power.

The frame of the structure is grounded, so the DC power supply is configured to turn on power transistor into the upper arm of the laser, and not into the simpler, opposite option. In addition, to avoid “tattooing” the patient, the current must be initially limited.

In a single-supply +5V circuit, current-sensing and current-limiting resistor R1 and p-channel MOSFET Q1 form the source follower (Figure 1). The MOSFET's gate voltage is slightly higher than the source voltage, so the transistor is partially on and the laser diode current creates a voltage drop across resistor R1. In the worst case, when Q1 is fully open, the maximum laser current is given by

R DS(SAT) = 25 mOhm - open channel resistance of the MOS transistor,
V LASER = 2.0 V - voltage on the laser diode.

The R DS(SAT) and V LASER values ​​were taken from the transistor and laser diode data sheets, respectively. The choice of resistor R1 is determined by the requirements for the laser current (in this case, 250 mA) taking into account the correction introduced by the forward voltage of the laser diode, a typical value of which is 2.0 V. Solving the equation for R1, we obtain:

where I LASER = 250 mA.

The resistance R DS(SAT) is so small that it can be ignored. With known values ​​of R1 and the maximum current of the laser diode, the power dissipated by R1 can be calculated using the formula

which means that a resistor with a permissible power dissipation of 800 mW will provide a small additional margin.

The laser current is set using a DAC, the output voltage of which is set ratiometrically. The +5 V source voltage is used as a reference here, so the DAC output tracks all power fluctuations. During operation, the required value of the control voltage is set at the ADC output. Divider R2, R3 scales this setting relative to the nominal +5 V supply.

For example, if the DAC output voltage is set to half scale, that is, +2.5 V, the voltage between R2 and R3, (or at the non-inverting input of op-amp IC1), will be +3.5 V. Included in the feedback loop, IC1 regulates the voltage at the gate of Q1 and , respectively, the current flowing through R1, Q1 and the laser diode. The circuit mode is stabilized when the feedback voltage becomes equal to +3.5 V. In this steady state, 5 V - 3.5 V = 1.5 V drops across resistor R1, and the current is 125 mA, that is, in the middle of the scale. Similarly, if the DAC output is set to a minimum value of 0 V, the voltage at the non-inverting input of IC1 will be +2 V. IC1 will increase the voltage at the gate of Q1 until the voltage drop across R1 increases to 3 V, and the current accordingly increases. up to 250 mA. This is the saturation point where Q1 is fully on and the forward voltage across the laser diode is +5V minus the voltage drop across R1.

IN full diagram elements R4 and C1 must be included, ensuring the stability of the control loop and having a cutoff frequency f equal to

Special attention should be paid to the process that occurs in the circuit during an abrupt change in the control voltage, during which the op-amp, which previously worked as an adder of the setpoint and feedback voltages, becomes a voltage follower, and a step tends to appear at its output. In this regard, in our example, capacitor C2 is added, forming a low-frequency filter for the setpoint voltage with a cutoff frequency

where R2||R3 = 12 kOhm.

If the cutoff frequency of this filter is much lower than the feedback loop bandwidth, the op amp will be able to track setpoint step changes with minimal overshoot during DAC switching.

R5 provides some bias to the op amp by ensuring that a small amount of current is always guaranteed to flow through resistor R1. When the DAC output is set to +5V full scale, the laser current driven by the op amp will always be slightly higher than the setting. Therefore, the op-amp output, trying to turn off Q1, will go into saturation. Without R5, the op amp's input offset voltage could be perceived as a false setpoint and cause Q1 to be turned on to restore balance.

This is one of the main reasons why ratiometric DAC switching is used. If the DAC's reference voltage were fixed, programming low currents would be virtually impossible. If the voltage at the DAC output is set slightly below the exact value of +5 V, then even with small fluctuations in the +5 V supply voltage, the control voltage will change quite significantly. However, in a ratiometric circuit, the DAC tracks changes in the +5 V supply voltage, and the relative control voltage at its output remains stable.

The price to pay for the ability to accurately set weak currents is bad ratio suppression of power ripples. However, in the medical application for which the laser was intended, the current regulation loop is itself part of the power regulation loop, and the power supply ripple in it is minimal. If necessary, you can add a small voltage stabilizer to the board, and at the cost of slightly increasing the number of components, you will receive stable, low-noise laser power.