Pigtailed Distributed Bragg Reflector (DBR) Single-Frequency Lasers, Butterfly Package

Webpage Features
	Clicking this icon opens a window that contains specifications and mechanical drawings.
	Clicking this icon allows you to download our standard support documentation.
Choose Item	Clicking the words "Choose Item" opens a drop-down list containing all of the in-stock lasers around the desired center wavelength. The red icon next to the serial number then allows you to download L-I-V and spectral measurements for that serial-numbered device.

Features

• Center Wavelengths from 761 nm to 1083 nm
• 14-Pin, Hermetically Sealed Butterfly Package
• Integrated Isolator, Thermoelectric Cooler (TEC), Thermistor, and Monitor Photodiode
• Typical Linewidths as Narrow as 1 MHz
• SM or PM Fiber Output with 2.0 mm Narrow Key FC/APC Connector

Applications

• High-Resolution Spectroscopy
• Time-Resolved Fluorescence and Raman Spectroscopy
• Metastable Helium Absorption Spectroscopy
• Optical Metrology and Sensors
• Rubidium or Cesium Atomic Clock Pump Sources
• Fiber Amplifier Seeding
• Nonlinear Frequency Conversion
• Laser Cooling and Trapping
• Free-Space Optical Communications
• Oxygen Sensing
• Low-Noise Laser Pumping
• Second-Harmonic Generation
• LIDAR
• Near-Infrared Spectroscopy (NIRS)
• Water Vapor Differential Absorption LIDAR (DIAL) Systems

Thorlabs' Distributed Bragg Reflector (DBR) lasers are narrow-linewidth, single-frequency (single-longitudinal-mode) laser diodes that have a monolithically integrated Bragg mirror outside of the active region. These lasers produce higher output powers than DFB lasers and achieve typical linewidths less than or equal to 10 MHz with an excellent side mode suppression ratio (50 dB typical). The output wavelengths of these lasers are current- and temperature-tunable. Please refer to the specifications for tuning coefficients. For a complete list of specifications for each DBR laser, click on the blue Info icons () in the tables below.

These DBR lasers are housed in a compact 14-pin, type-1 butterfly package, enabling compatibility with any standard 14-pin laser diode mount (such as item # LM14S2). The butterfly package includes an integrated thermoelectric cooler (TEC), thermistor, monitor photodiode, and a single mode or polarization-maintaining output fiber with an FC/APC connector. DBR lasers are extremely sensitive to back reflections, which necessitates the use of the angled FC/APC connector. For additional protection from back reflections, each of the butterfly package DBR lasers includes an internal optical isolator.

While the center wavelengths are listed for the laser diodes below, they are only the typical values. The center wavelength of a particular unit varies from production run to production run, so the diode you receive may not operate at the typical center wavelength. After clicking "Choose Item" below, a list will appear that contains the center wavelength, output power, and operating current of each in-stock unit. Clicking on the red Docs icon () next to the serial number provides access to a PDF with serial-number-specific L-I-V and spectral characteristics. For additional single frequency laser options, Thorlabs also offers external cavity, butterfly-packaged single frequency lasers. These lasers offer narrower linewidths compared to our DBR lasers.

These DBR lasers are compatible with Thorlabs' line of laser diode drivers and temperature controllers. To achieve the narrowest possible linewidth, we recommend using a driver with low drive current noise, such as our LDC series of drivers.

We recommend cleaning the fiber connector before each use if there is any chance that dust or other contaminants may have deposited on the surface. The laser intensity at the center of the fiber tip can be very high and may burn the tip of the fiber if contaminants are present. While the connector is cleaned and capped before shipping, we cannot guarantee that it will remain free of contamination after it is removed from the package. We also recommend that the laser is turned off when connecting or disconnecting the device from other fibers.

Type 1 Butterfly Package Pin Diagram

Click to Enlarge

ECL, DFB, VHG-Stabilized, and DBR Single-Frequency Lasers

Click to Enlarge
Figure 1: ECL Lasers have a Grating Outside of the Gain Chip

A wide variety of applications require tunable single-frequency operation of a laser system. In the world of diode lasers, there are currently four main configurations to obtain a single-frequency output: external cavity laser (ECL), distributed feedback (DFB), volume holographic grating (VHG), and distributed Bragg reflector (DBR). All four are capable of single-frequency output through the utilization of grating feedback. However, each type of laser uses a different grating feedback configuration, which influences performance characteristics such as output power, tuning range, and side mode suppression ratio (SMSR). We discuss below some of the main differences between these four types of single-frequency diode lasers.

External Cavity Laser
The External Cavity Laser (ECL) is a versatile configuration that is compatible with most standard free space diode lasers. This means that the ECL can be used at a variety of wavelengths, dependent upon the internal laser diode gain element. A lens collimates the output of the diode, which is then incident upon a grating (see Figure 1). The grating provides optical feedback and is used to select the stabilized output wavelength. With proper optical design, the external cavity allows only a single longitudinal mode to lase, providing single-frequency laser output with high side mode suppression ratio (SMSR > 45 dB).

One of the main advantages of the ECL is that the relatively long cavity provides extremely narrow linewidths (<1 MHz). Additionally, since it can incorporate a variety of laser diodes, it remains one of the few configurations that can provide narrow linewidth emission at blue or red wavelengths. The ECL can have a large tuning range (>100 nm) but is often prone to mode hops, which are very dependent on the ECL's mechanical design as well as the quality of the antireflection (AR) coating on the laser diode.

Click to Enlarge
Figure 2: DFB Lasers Have a Bragg Reflector Along the Length of the Active Gain Medium

Distributed Feedback Laser
The Distributed Feedback (DFB) Laser (available in NIR and MIR) incorporates the grating within the laser diode structure itself (see Figure 2). This corrugated periodic structure coupled closely to the active region acts as a Bragg reflector, selecting a single longitudinal mode as the lasing mode. If the active region has enough gain at frequencies near the Bragg frequency, an end reflector is unnecessary, relying instead upon the Bragg reflector for all optical feedback and mode selection. Due to this “built-in” selection, a DFB can achieve single-frequency operation over broad temperature and current ranges. To aid in mode selection and improve manufacturing yield, DFB lasers often utilize a phase shift section within the diode structure as well.

The lasing wavelength for a DFB is approximately equal to the Bragg wavelength:

where λ is the wavelength, n_eff is the effective refractive index, and Λ is the grating period. By changing the effective index, the lasing wavelength can be tuned. This is accomplished through temperature and current tuning of the DFB.

The DFB has a relatively narrow tuning range: about 2 nm at 850 nm, about 4 nm at 1550 nm, or at least 1 cm^-1 in the mid-IR (4.00 - 11.00 µm). However, over this tuning range, the DFB can achieve single-frequency operation, which means that this is a continuous tuning range without mode hops. Because of this feature, DFBs have become a popular and majority choice for real-world applications such as telecom and sensors. Since the cavity length of a DFB is rather short, the linewidths are typically in the 1 MHz to 10 MHz range. Additionally, the close coupling between the grating structure and the active region results in lower maximum output power compared to ECL and DBR lasers.

Click to Enlarge
Figure 3: VHG Lasers have a Volume Holographic Grating Outside of the Active Gain Medium

Volume-Holographic-Grating-Stabilized Laser
A Volume-Holographic-Grating-(VHG)-Stabilized Laser also uses a Bragg reflector, but in this case a transmission grating is placed in front of the laser diode output (see Figure 3). Since the grating is not part of the laser diode structure, it can be thermally decoupled from the laser diode, improving the wavelength stability of the device. The grating typically consists of a piece of photorefractive material (typically glass) which has a periodic variation in the index of refraction. Only the wavelength of light that satisfies the Bragg condition for the grating is reflected back into the laser cavity, which results in a laser with extremely wavelength-stable emission. A VHG-Stabilized laser can produce output with a similar linewidth to a DFB laser at higher powers that is wavelength-locked over a wide range of currents and temperatures.

Click to Enlarge
Figure 4: DBR Lasers have a Bragg Reflector Outside of the Active Gain Medium

Distributed Bragg Reflector Laser
Similar to DFBs, Distributed Bragg Reflector (DBR) lasers incorporate an internal grating structure. However, whereas DFB lasers incorporate the grating structure continuously along the active region (gain region), DBR lasers place the grating structure(s) outside this region (see Figure 4). In general a DBR can incorporate various regions not typically found in a DFB that yield greater control and tuning range. For instance, a multiple-electrode DBR laser can include a phase-controlled region that allows the user to independently tune the phase apart from the grating period and laser diode current. When utilized together, the DBR can provide single-frequency operation over a broad tuning range. For example, high end sample-grating DBR lasers can have a tuning range as large as 30 - 40 nm. Unlike the DFB, the output is not mode hop free; hence, careful control of all inputs and temperature must be maintained.

In contrast to the complicated control structure for the multiple-electrode DBR, a simplified version of the DBR is engineered with just one electrode. This single-electrode DBR eliminates the complications of grating and phase control at the cost of tuning range. For this architecture type, the tuning range is similar to a DFB laser but will mode hop as a function of the applied current and temperature. Despite the disadvantage of mode hops, the single-electrode DBR does provide some advantages over its DFB cousin, namely higher output power because the grating is not continuous along the length of the device. Both DBR and DFB lasers have similar laser linewidths. Currently, Thorlabs offers only single-electrode DBR lasers.

Conclusion
ECL, DFB, VHG, and DBR laser diodes provide single-frequency operation over their designed tuning range. The ECL can be designed for a larger selection of wavelengths than either the DFB or DBR. While prone to mode hops, it also provides the narrowest linewidth (<1 MHz) of the three choices. In appropriately designed instruments, ECLs can also provide extremely broad tuning ranges (>100 nm).

The DFB laser is the most stable single-frequency, tunable laser of the four. It can provide mode-hop-free performance over its entire tuning range (<5 nm), making it one of the most popular forms of single-frequency laser for much of industry. It has the lowest output power due to inherent properties of the continuous grating feedback structure.

The VHG laser provides the most stable wavelength performance over a range of temperatures and currents and can provide higher powers than are typical in DFB lasers. This stability makes it excellent for use in OEM applications.

The single-electrode DBR laser provides similar linewidth and tuning range as the DFB (<5 nm). However, the single-electrode DBR will have periodic mode hops in its tuning curve.

Laser Diode and Laser Diode Pigtail Warranty

When operated within their specifications, laser diodes have extremely long lifetimes. However most failures occur from mishandling or operating the lasers beyond their maximum ratings. Laser Diodes are among the most static sensitive devices currently made. Since Thorlabs does not receive any warranty credit from our laser manufacturers we cannot guarantee the lasers after their sealed package has been open. Thorlabs will be happy to extend a full refund or credit for any lasers returned in their original sealed package.

Handling and Storage Precautions

Because of their extreme susceptibility to damage from electrostatic discharge (ESD), care should be taken whenever handling and operating laser diodes:

• Wrist Straps: Use grounded anti-static wrist straps whenever handling diodes.
• Anti-static Mats: Always work on grounded anti-static mats.
• Storing Lasers: When not in use, short the leads of the laser together to protect against ESD damage.

Operating and Safety Precautions

Use an appropriate driver, laser diodes require precise control of operating current and voltage to avoid overdriving the lasers. In addition, the laser driver should provide protection against power supply transients. Select a laser driver appropriate for your application. Do not use a voltage supply with a current limiting resistor since it does not provide sufficient regulation to protect the laser.

• Power Meters: When setting up and calibrating a laser with its driver, use a NIST-traceable power meter to precisely measure the laser output. It is usually safest to measure the laser output directly before placing the laser in an optical system. If this is not possible, be sure to take all optical losses (transmissive, aperture stopping, etc.) into consideration when determining the total output of the laser.
• Reflections: Flat surfaces in the optical system in front of a laser diode can cause some of the laser energy to reflect back onto the laser’s monitor photodiode giving an erroneously high photodiode current. If optical components are moved within the system and energy is no longer reflected onto the monitor photodiode, a constant power feedback loop will sense the drop in photodiode current and try to compensate by increasing the laser drive current and possibly overdriving the laser. Back reflections can also cause other malfunctions or damage to laser diodes. To avoid this, be sure that all surfaces are angled 5-10° and when necessary, use optical isolators to attenuate direct feedback into the laser.
• Heat Sinks: Laser lifetime is inversely proportional to operating temperature. Always mount the laser in a suitable heat sink to remove excess heat from the laser package.
• Voltage and Current Overdrive: Be careful not to exceed the maximum voltage and currents even momentarily. Also, reverse voltages as little as 3 V can damage a laser diode.
• ESD Sensitive Device: Even when a laser is operating it is susceptible to ESD damage. This is particularly aggravated by using long interface cables between the laser and its driver due to the inductance that the cable presents. Avoid exposing the laser or its mounting apparatus to ESDs at all times.
• ON/OFF and Power Supply Coupled Transients: Because of their fast response times, laser diodes can be easily damaged by transients less than 1 µs. High current devices such as soldering irons, vacuum pumps, fluorescent lamps, etc., can cause large momentary transients; use surge-protected outlets.

If you have any questions regarding laser diodes, please call your local Thorlabs Tech Support office for assistance.