Narrow linewidth single frequency lasers play an irreplaceable role in precision measurement, optical communication, sensing, and other fields due to their high spectral purity and frequency stability.

The core of a narrow linewidth single frequency laser is to achieve single longitudinal mode oscillation and maintain the frequency stability of the output laser. The key technologies include:

Single longitudinal mode selection mechanism:

Distributed Feedback (DFB) structure: Provides selective reflection through Bragg gratings, allowing only specific wavelengths (longitudinal modes) to vibrate.

External cavity feedback (ECL): Using external mirrors or fiber Bragg gratings to form short cavities and suppress multimode competition.

Saturated absorber (such as semiconductor saturable absorber mirror SAS): dynamically suppresses multi-mode noise and stabilizes single frequency output.

Frequency stabilization technology:

Active feedback control: Real time monitoring of frequency offset and adjustment of cavity length or current through frequency discrimination modules (such as beat detection or molecular absorption spectroscopy).

Passive temperature control: using a constant temperature bath or thermoelectric cooler (TEC) to reduce the impact of environmental temperature fluctuations on refractive index.

Narrow linewidth source: Narrowing linewidth can be achieved by extending cavity length or increasing reflectivity.

2. Stability performance of narrow linewidth single frequency laser:

(1) Frequency stability

Short term stability: Due to fluctuations in cavity length and current noise, the typical short-term linewidth can reach the kHz level.

Long term stability: Through active feedback or temperature control, it is possible to achieve a frequency drift of<1MHz in minutes to hours.

Environmental sensitivity: Temperature changes may cause frequency shifts of several GHz, requiring precise temperature control.

(2) Power stability

The fluctuation of output power is usually less than 0.1% (RMS), which can be further suppressed through APC (Automatic Power Control) circuit.

(3) Anti-interference ability

Mode competition suppression: By designing a high gain threshold difference to suppress edge modes, single frequency output is ensured.

External disturbance isolation: measures such as using isolation platforms and shielding electromagnetic interference (EMI) are taken to reduce the impact of environmental noise.