Wavelength Tunable Lasers

The Broadsweepers series is a new family of tunable semiconductor lasers intended for applications that require fast and precision wavelength tuning with high sweep-to-sweep reproducibility of the "instantaneous" wavelength. Among all possible applications, the most important are Optical Coherence Tomography (including Full Field OCT), biomedical imaging, interferometry, optical spectroscopy, fiber-optic sensing and optical component characterization.

The optical scheme of the Broadsweeper is based on an external fiber-optic ring cavity and a broadband Semiconductor Optical Amplifier (SOA), working as a gain medium. The wide bandwidth feature of the SOA module and its high fiber-to-fiber gain allow reaching a wavelength tuning range of more than 50 nm at 3 mW of the output power.

The wavelength tuning technique involves the use of an Acousto-Optical Tunable Filter (AOTF) with a very narrow spectral passband ranging from 0.2 to 0.8 nm (FWHM). The AOTF is actively temperature controlled for high spectral stability of laser radiation. Since the laser cavity contains no mechanically moving components, high accuracy of wavelength selectivity and excellent wavelength reproducibility in sweep operation are ensured. Due to the perfect AOTF tuning characteristic, the laser provides k-linear wavelength tuning over a wide spectral range.

As well as the SOA and the AOTF, the other important elements of the laser are a fiber-optic coupler, optical isolator and in-line optical power monitor. All of them feature a unique customized design perfectly fitted for broadband spectral applications. Collimating optics used with the AOTF is relied on high-quality aspherical lens. This optics is aberration-free that allows obtaining not only a well-collimated laser beam required for effective operation of the AOTF but also maximum efficiency of coupling the light into the output optical fiber. The filter and the optics are packaged into one monolithic metal housing, thereby ensuring reliable day-after-day operation without misalignment. The external cavity of the laser uses a PANDA-type polarization maintaining (PM) fiber. This provides a well-defined state of polarization as well as high stability of laser polarization in time and under different ambient conditions. The only front-panel optical port delivers an optical signal with ultra-low amplified spontaneous emission (< -50 dB) and a polarization extinction ratio (PER) of min. 18 dB. Most of the fiber-optic components are built on the fast-axis-blocked technology that also guarantees high values of the PER at the laser output.

The output polarization is provided in the slow axis of the fiber that is precisely aligned to the connector key.

The laser is housed in a compact metal case suitable for applications on the bench and in the rack. The device has a modular design that incorporates several plug-in modules (power supplies, tunable optical module, current and temperature driving module, central processing unit, etc.) into one single mainframe. Our driving electronics provides precise, reliable and safe control of the laser in all modes of operation. All the necessary laser diode protective measures such as transient suppression, over-temperature protection, open-circuit protection and laser current limit are implemented. The optical power control loop in combination with the very fast laser current source adjusted for automatic-power-control mode allow operation with a flat-top-shaped tuning characteristic at all specified sweep speeds.

The laser provides the following modes of operation:

• CW operation at any single wavelength within the full tuning range. The operating wavelength is adjustable from the front panel or from a computer. Under computer control, typical switching between two different wavelengths is done in less than 100 ms. The user can select any wavelength within the full wavelength range with a 50-pm resolution.

• Continuous sweeps over the full tuning range or over the band of interest (within the full tuning range) not shorter than 5 nm. Both the internal triggering and the external triggering are available.

• Continuous switching between any two wavelengths within the full tuning range at a certain repetition frequency. The range of frequencies includes 13 factory-set values. Customized settings for the repetition frequency are possible upon request.

When internally triggered, the device produces synchronizing pulses. BNC-connectors necessary to synchronize the laser with your measuring equipment are located on the rear panel of the device. In the external triggering mode, the device responds to incoming TTL-compatible trigger signals.

The Broadsweeper offers the maximum output power of 3 mW. For powerful applications, the device can additionally be equipped with an optical power booster elevating the power up to 20 mW.

The laser output is performed through the front-panel high precision PM optical socket for an FC/APC connector with the narrow key (2.0 mm). The device is supplied with a PM optical patch cable. An SM optical patch cable is also available on request.

Remote Control Capability

The device has an RS-232 DTE port for remote control from a computer. The necessary connectivity software is supplied with the instrument.

Laser Safety Measures

To fulfill the requirements of IEC 60825-1 Ed. 2 2007-03, the instrument is equipped with laser safety measures including: the master key control, remote interlock connection, visual/audible alarm, informational warning stickers, etc.

Standard Models Available For Ordering

Depending on the spectral band and sweep speed, there are several models of the product to choose from. Refer to the table below for the standard versions of the product.

* INCLUDES INTERNAL OPTICAL POWER BOOSTER

General Specifications

* FOR MODELS WITH INTERNAL OPTICAL POWER BOOSTER

Product Customization Capabilities

We offer product customization services. A number of the operating characteristics of the product (e.g. the output power level, target wavelengths for the tuning range, the sweep speed limits, etc.) can be modified to meet your requirements. Please contact us for further discussion of your tunable laser requirements.