Optical injection locking has been demonstrated to be effective as a means of stabilizing the wavelength of light emitted by a vertical-cavity surface-emitting laser (VCSEL) that is an active element in the frequency-control loop of an opto-electronic oscillator (OEO) designed to implement an atomic clock based on an electromagnetically-induced-transparency resonance. This particular optical-injection-locking scheme is expected to enable the development of small, lowpower, high-stability atomic clocks that would be suitable for use in applications involving precise navigation and/or communication.
In one essential aspect of operation of an OEO of the type described above, a microwave modulation signal is coupled into the VCSEL. Heretofore, it has been well known that the wavelength of light emitted by a VCSEL depends on its temperature and drive current, necessitating thorough stabilization of these operational parameters. Recently, it was discovered that the wavelength also depends on the microwave power coupled into the VCSEL. Inasmuch as the microwave power circulating in the frequency-control loop is a dynamic frequency-control variable (and, hence, cannot be stabilized), there arises a need for another means of stabilizing the wavelength.
The present optical-injection-locking scheme satisfies the need for a means to stabilize the wavelength against microwave-power fluctuations. It is also expected to afford stabilization against temperature and current fluctuations. In an experiment performed to demonstrate this scheme, wavelength locking was observed when about 200 μW of the output power of a commercial tunable diode laser was injected into a commercial VCSEL, designed to operate in the wavelength range of 795±3 nm, that was generating about 200 μW of optical power. (The use of relatively high injection power levels is a usual practice in injection locking of VCSELs.)
This work was done by Dmitry Strekalov, Andrey Matsko, Anatoliy Savchenkov, Nan Yu, and Lute Maleki of Caltech for NASA’s Jet Propulsion Laboratory. NPO-43454
This Brief includes a Technical Support Package (TSP).
Optical Injection Locking of a VCSEL in an OEO
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Overview
The document titled "Optical Injection Locking of a VCSEL in an OEO" (NPO-43454) is a Technical Support Package from NASA's Jet Propulsion Laboratory, detailing advancements in the stabilization of Vertical Cavity Surface Emitting Lasers (VCSELs) for use in optoelectronic oscillators (OEOs). The primary challenge addressed is the sensitivity of VCSEL wavelengths to variations in temperature, current, and microwave power, which can hinder their performance in active loop configurations, particularly in applications like EIT-based atomic clocks.
The problem arises because the wavelength of a VCSEL is significantly influenced by its operating conditions. Specifically, fluctuations in microwave power, which are dynamic and cannot be easily stabilized, lead to undesirable changes in the optical frequency of the VCSEL. This variability poses a critical obstacle for reliable operation in precision timing applications.
To mitigate these issues, the document discusses the technique of optical injection locking, where a VCSEL is synchronized to a master laser. This method has been shown to enhance the performance of VCSELs by increasing their bandwidth and reducing frequency chirp. By employing a Newfocus Vortex laser as the master, the researchers coupled approximately 200 μW of optical power into a slave VCSEL (model ULM795-03-TN-S46FTT), achieving a stabilization of the optical frequency against fluctuations in microwave power, temperature, and current.
The novelty of this approach lies in its application to the specific problem of wavelength tuning in VCSELs, which is critical for their deployment in active loop configurations of atomic clocks. The successful demonstration of optical injection locking in this context represents a significant advancement in the field, potentially enabling more reliable and precise timing systems.
The document emphasizes the broader implications of this research, suggesting that the findings could have wider technological, scientific, and commercial applications beyond aerospace. It serves as a resource for those interested in the innovative technologies being developed under NASA's Commercial Technology Program, highlighting the potential for collaboration and further exploration in this area.
For additional inquiries or information regarding this research, the document provides contact details for the Innovative Technology Assets Management at JPL.
