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The ULN15TK laser can be mounted to an optical table using four 1/4"-20 cap screws. The ULN15TK is pictured with a P3-1550PM-FC-5 PM fiber patch cable and three CA2912 SMA cables, which are connected to the optical output and analog modulation ports, respectively.

Reza Salem
BU Leader, Fiber Lasers

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Thorlabs' ULN15TK Turnkey, Ultra-Low-Noise (ULN) Laser System is a ready-to-use laser system that integrates our ULN15PC laser, which has a patented fiber Bragg grating (FBG) based design, with a low-noise driver and temperature stabilization inside of a benchtop housing. This turnkey laser system provides single-frequency emission with relative intensity noise below -160 dBc/Hz and typical (Lorentzian) linewidths of 100 Hz. Factory-set for optimized performance, this laser offers typical optical output powers of 120 mW with a side mode suppression ratio (SMSR) of 70 dB.

The optical output of this laser is fiber-coupled via an FC/APC bulkhead (2.0 mm narrow key) output connector. For best performance, we recommend connecting our PM FC/APC fiber patch cables that contain PM1550-XP fiber, such as the P3-1550PM-FC-1 patch cable. Note that the polarization axis is aligned with the narrow key of the bulkhead connector.

The system is powered by a 12 VDC, 4 A input. A DS12 power supply is provided with each laser; see the Shipping List tab for a complete list of items included with the device.

Single-Frequency Operation
Factory-set for single-frequency operation, the ULN15TK laser has a preset drive current and FBG temperature. These operating conditions are selected to minimize the laser linewidth while also providing the highest output power and long-term stability.

To achieve the narrow linewidth of the ULN15PC laser, this turnkey ULN laser includes drive electronics that are designed to minimize the current noise. The drive electronics also includes a thermal stabilization system that controls the internal temperature settings of the laser and ensures long-term power and wavelength stability when the system is used in standard laboratory environments. A fiber isolator is also integrated at the output of the laser in order to minimize the impact of any back-reflected light on the laser.

When this turnkey laser is enabled using the push-button switch on the front panel (see Front & Back Panels tab), the laser operates at the preset current level. Each laser is shipped with a test data sheet taken at the preset operating conditions; click here for a sample data sheet. For typical frequency noise and relative noise intensity plots, see the Graphs tab. Please note that the laser requires a 10 minute warm-up after it has been enabled in order to reach its specified linewidth.

Analog Modulation
By controlling the laser drive current or temperature, the laser wavelength can be tuned free of mode-hopping within a small range around its set-point. Three analog modulation ports (SMA Female) are included on the front panel (see the Front & Back Panels tab). Two of the ports allow the laser current to be modulated by ±10 mA around the current set point: of these, the port labelled "AC Current" can support modulation frequencies up to 20 MHz, and the port labelled "DC Current" accepts frequencies from DC to 5 MHz. The third port, which is labelled "Temp", controls the FBG temperature and accepts modulation frequencies from DC to 1 Hz. To see how the laser wavelength can be tuned around its set-point, please see the wavelength tuning plots provided in the Graphs tab.

Each modulation port accepts a -5 V to 5 V input signal. To convert the modulation voltage into a current or temperature change, see the Specs tab.

Remote Operation
Remote operation is also possible by connecting the laser to a PC (not included) via the USB port on the back of the unit and using a command line interface. In addition to basic functions such as turning the laser on and off or reading status indicators, the command line enables the user to modify the laser operating set-points. A USB-AB-72 USB 2.0 Type-A to Mini-B Cable is included with each device.

Adjusting the laser parameters within a limited range around the set-point can be used to tune the center wavelength while staying in the single-frequency operating regime. If the setpoints are changed outside of this limited range of values, the lasing spectrum of the laser may change between single longitudinal mode and multimode; see the full ULN15PC web presentation for a detailed discussion on single-mode operation. Typical performance plots that demonstrate the laser's center wavelength tuning and the single-mode operating regions can be found on the Graphs tab. Please note that specific performance data is provided on the datasheet shipped with each device.

A 9-Pin female D-Sub connector is also included on the back panel of the system for RS-485 communication protocol. Please refer to the Pin Diagrams tab for the pin assignment of the connector.

Mounting
For mounting to an optical table, the compact housing of this benchtop ULN laser features four clearance holes each for M6 and 1/4-20" cap screws.

The plots below represent the typical performance of the ULN15TK ultra-low-noise laser system. Specific performance data is provided on the datasheet shipped with each device; click here for a sample data sheet.

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Example frequency noise data for a ULN15TK laser system operated at the factory-set conditions. Using the high-frequency white noise level estimation described in the ULN15PC manual, this ULN15TK laser has an approximate Lorentzian linewidth of 70 Hz.

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The typical low-frequency relative intensity noise (RIN) for a ULN15TK laser system operated at the factory-set conditions.

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The typical single mode operating regions for a ULN15TK laser system operated at a Fiber Bragg Grating temperature (T_FBG) of 27 °C. Multimode regions have been removed.

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The center wavelength (λ_c) tuning with changes in the pump current and Fiber Bragg Grating temperature (T_FBG). Multimode regions have been removed.

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The typical spectrum for a ULN15TK laser system operated at the factory-set conditions. This measurement is limited by the 0.02 nm optical spectrum analyzer resolution bandwidth.

The ULN15TK Turnkey Ultra-Low-Noise Laser System ships with the following components:

• Ultra-Low-Noise Laser in Benchtop Housing
• DS12 Power Supply
• USB-AB-72 USB 2.0 Type-A to Mini-B Cable, 72" (1.83 m) Long
• FBC250 Connector and Bulkhead Cleaner

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Experimental Setup for Laser Stabilization

Laser Stabilization

The ULN15TK turnkey ultra-low noise laser offers exceptional optical spectral purity and is configured for out-of-the-box use with little setup effort. However, for the most demanding applications, such as optical clocks and high-resolution spectroscopy, active electronic feedback may be required to further suppress technical noise and drifts. This turnkey laser conveniently provides multiple high-bandwidth analog modulation ports for locking to external optical references such as an optical cavity or an atomic/molecular transition.

Thorlabs offers low loss supermirrors on their own or integrated into custom reference cavities. In the figure to the right, we show an example of how the Pound-Drever-Hall (PDH) locking scheme is used to lock the ULN15TK laser to a reference cavity comprised of XM12R8 and XM12P8 crystalline supermirrors attached to an ultra-low expansion glass spacer. The RF modulation input conveniently permits the PDH sidebands to be generated without an external optical modulator. Demodulation of the reflected signal from the cavity yields an error signal which can be processed with a servo filter to maintain resonance with the optical cavity. This turnkey laser provides a high-bandwidth DC-coupled current modulation port to correct for fast fluctuations, and a slower temperature modulation port with larger range to correct for slower drifts.