Application Cases

Experiment Name: Theoretical and Experimental Study of Intensity Noise of Signal and Idle Beams in SRO

Test Purpose: The intensity noise characteristics of the signal and idle beams output by SRO were investigated. First, the intensity noise of the signal and idle beams was theoretically studied, and the factors affecting the intensity noise of the signal and idle beams and the methods to reduce the intensity noise were analyzed. Then, the intensity noise of the signal and idle beams was optimized by controlling the temperature of the MgO:PPLN crystal and the modulation frequency of the signal applied to the etalon.

Testing Equipment: High-voltage power amplifier, laser, optical isolator, spectrum analyzer, photodetector, etc.

Experimental Process:

Figure 1: Experimental setup for obtaining infrared laser using SRO

The experimental setup for obtaining continuous wide-tuning infrared laser using SRO and optimizing the intensity noise of signal and idle beams is shown in Figure 2. The pump light source is a homemade 1.06μm Nd:YVO4 laser from the laboratory. First, it passes through a half-wave plate (HWP1) and an optical isolator (OI) to prevent reflected light from affecting the laser, and then through HWP2 to control the polarization direction of the pump light entering the SRO cavity. The SRO used in the experiment is designed as a symmetrical four-mirror ring structure, and the specific parameters of the SRO cavity are the same as those in Chapter 3. To obtain mode-hop-free signal light, a lithium niobate electro-optic crystal with dimensions of 2mm (T) × 5mm (W) × 1mm (L) is used as an etalon, which is inserted between M3 and M4, and the single-longitudinal-mode operation of the signal light is realized by the mode selection function of the etalon. The signal light output from M4 is reflected by M5, and after passing through HWP and PBS, most of the signal light is injected into the coherent power meter to measure its output power. The remaining part of the signal light is injected into the self-homodyne detection system to measure and analyze the intensity noise of the signal light. This detection system consists of HWP, PBS, and photodetectors PD1 and PD2. The signal light entering PD1 and PD2 is converted into current and input into an add-subtract amplifier, and the sum and difference signals are measured by a spectrum analyzer (SA). The sum and difference represent the intensity noise of the signal light and the corresponding SNL, respectively. The DC signal output from PD2 is demodulated by LA to obtain the error signal, which is then input into PID for processing. The control signal output from PID is amplified by a high-voltage power amplifier (HV) and applied to the PZT to achieve cavity length control.

Experimental Results:

Figure 2: Intensity noise spectrum of pump laser before and after passing through the SRO cavity

Firstly, by locking the transmission peak of the intracavity etalon to the resonance frequency of the SRO, continuous wide-tuning infrared laser output without mode hopping was realized. To obtain low-noise infrared laser output, it is necessary to study the intensity noise of the signal and idle beams. When studying the intensity noise of the laser output by the SRO, the intensity noise of the pump laser is an important influencing factor. Therefore, the intensity noise of the pump laser under different conditions was first measured experimentally, as shown in Figure 2. Curve (i) represents the SNL, curve (ii) represents the normalized intensity noise of the pump light before the SRO cavity, and curve (iii) represents the normalized intensity noise of the pump light after a single pass through the SRO cavity. It can be seen from the figure that the intensity noise of the pump light reaches the SNL after 7MHz. Moreover, in the range of 300kHz to 5MHz, the intensity noise of curve (iii) is lower than that of curve (ii). This is because the SRO cavity design is similar to that of a mode cleaner and has a certain mode filtering capability, which can filter the intensity noise of the pump light to some extent, resulting in a reduction in the intensity noise of the pump laser after passing through the SRO cavity.

Recommended Power Amplifier: ATA-4315

Figure: ATA-4315 High-Voltage Power Amplifier Specifications

This material is organized and published by Aigtek Antai Electronics. For more case studies and product details, please continue to follow us. Xi'an Aigtek Antai Electronics has become a widely recognized instrument and equipment supplier with a broad range of product lines and considerable scale in the industry, and all sample machines are available for free trial.