Fabry–Perot Laser Diodes
A Fabry–Pérot laser diode (FP laser diode) is the most common type of laser diode, having a laser resonator which is a Fabry–Pérot interferometer. This means that substantial light reflections occur at both ends, but not within the gain medium. In contrast to that, the resonator of a distributed Bragg reflector laser exhibits a distributed reflection throughout the gain medium, usually created by a grating structure.
In the simplest case, the end reflections in an Fabry–Pérot laser are Fresnel reflections at the interface between the semiconductor device structure and air. Note that the refractive index contrast at these locations is quite high, leading to a substantial reflectivity without any additional measures. If that principle is utilized on both sides, the threshold pump power may already be low enough, and about half of the optical output power is obtained at each side.
In order to obtain the total output power on one side, which is usually preferable, or for optimizing the output power via a lower threshold pump power, one often increases the reflectivity on the side opposite to the output side, e.g. with a semiconductor Bragg mirror structure. In the specific case of a distributed Bragg reflector laser (DBR lasers), increased reflectivities are obtained with Bragg mirrors, or with a Bragg mirror on only one side.
Mode Structure, Beam Quality and Optical Spectrum
A Fabry–Pérot laser diode may emit only on fundamental spatial resonator modes, which leads to a relatively high beam quality, or also on higher-order spatial modes, resulting in a poorer beam quality. The most common example for the latter case is a broad area laser diode. Generally, higher output power (multiple watts) can be achieved when allowing for spatially multimode emission, usually in an active area with increased dimensions.
Even if lasing is restricted to fundamental spatial modes, it may occur on more than one longitudinal mode. Despite the relatively short length of the laser resonator, the free spectral range of the resonator may be small enough compared with the gain bandwidth to allow for that phenomenon. As a result, the laser output spectrum exhibits multiple optical frequencies. (These typically have a spacing of the order of 100 GHz.) It may also happen that emission occurs on a single mode at a time, but temperature changes lead to occasional mode hops to neighbored resonator modes, or also to occasional oscillation on two modes.
For realizing a narrow linewidth laser, one needs to achieve single-mode operation, e.g. by restricting the drive current or the resonator length. (The output can then still contain some weak sub-threshold fluorescence on several other modes.) Another frequently used technique is not to use a Fabry–Pérot design, but instead a distributed Bragg reflector (DFB) design.
Due to the short resonator length, the substantial round-trip losses of the resonator and the moderate intracavity power, the laser linewidth is often substantial (multiple megahertz) even in the case of stable single-mode operation. The linewidth may be substantially reduced by coupling to or integration into an external optical resonator. This leads to the concept of an external-cavity diode laser.
Emission Wavelengths of FP Laser Diodes
Fabry–Pérot laser diodes are available with a very wide range of emission wavelengths from the visible region to the mid and far infrared. For the longest output wavelengths, they can be realized as quantum cascade lasers.
There are also semiconductor optical amplifiers which are realized as Fabry–Pérot amplifier. Here, relatively weak and reflections are utilized such that the device stays below the laser threshold. Still, those reflections can substantially increase the amplifier gain.
QPC Lasers full vertical integration from epitaxy through packaging allows us to offer standard and custom diode solutions in packages ranging from mini-mounts to complete OEM light engines that provide performance without compromise.
SHIPS TODAY: AeroDIODE offers a wide range of solutions combining Fabry–Pérot fiber-coupled laser diodes with various models of CW or pulsed laser diode driver. The user adjusts the temperature which tunes the emission wavelength over a wavelength range of more than 10 nm. Many butterfly laser diode models are available at many wavelengths such as 808 nm, 1030 nm, 1064 nm, 1310 nm, 1550 nm and 1650 nm. The 1064 nm laser diodes are also available with a FBG (Fiber Bragg Grating) adapted for Nd:YAG or Nd:YVO4 laser seeding.
See also our tutorial on fiber-coupled laser diodes.
Sacher Lasertechnik has various kinds of Fabry–Pérot laser diodes which emit spatially single mode.
Available wavelengths are 375–440 nm and 635–1710 nm. Output powers range from 1 mW to 200 mW. The most common types of laser mount are 5.6–mm TO-can and 9–mm TO-can.
Typical geometrical sizes of the laser chip are 1000 µm × 500 µm × 200 µm (length × width × height). Depending on the chip length, Fabry Perot lasers operate longitudinally single- or multimode.
Serving North America, RPMC Lasers offers one of the widest wavelength selections of Fabry–Pérot laser diodes available, ranging from the UV through the IR. These products include fiber-coupled and free-space single-mode diode lasers, multimode single emitters, multi-emitter fiber-coupled modules, laser diode bars, and laser diode stacks. RPMC can provide standard and custom laser diode solutions for any problem. Let us know what you need and we'll help you find it!
Eblana Photonics designs and manufacture FP laser diodes spanning the NIR to MIR region (650 nm – 12 μm), available in a wide variety of package types and configurations. We leverage our unique epistructure design to deliver a cost effective laser source with high power and excellent spectral characteristics, facilitating applications in free space coms, environmental gas monitoring and beyond.
Eagleyard offers Fabry–Pérot laser diodes with up to 800 mW output power at 808 nm, and versions for other output wavelengths.
TOPTICA offers a large variety of wavelength-selected single-mode laser diodes. Among more standard laser diodes you will also find "rarities", i.e. diodes with output wavelengths that only TOPTICA provides. The diodes can be purchased separately. In addition TOPTICA can integrate any diode from the stock lists into a tunable diode laser system: Fabry–Pérot or AR-coated laser diodes may be integrated into a diode laser systems, DFB/DBR laser diodes into a DFB pro and a tapered amplifier into an TA system.
Our broad gain illuminators are Fabry–Pérot lasers designed for maximum width of the gain profile. They can be used as broad spectrum illuminators for spectroscopy or imaging. Combined with an anti-reflection coating, they are suitable for use in an external cavity to obtain a tunable laser with wide tuning range. Their wide and flat gain spectrum can also be suitable to develop frequency combs.
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