New breakthroughs in LiNbO3 modulator

New breakthroughs in LiNbO3 modulator
Recently, Chinese researchers have released a core invention patent on the PDH laser frequency locking technology. A PDH laser frequency locking system based on nonlinear SOA (Semiconductor Optical Amplifier) to generate sidebands. This patent aims to address several key pain points in the traditional PDH (Pound-Drever-Hall) laser frequency locking system due to the use of lithium niobate (LiNbO3 modulator) and other electro-optic modulator.
1. Main problems of the traditional solution include:
1.1 High cost and complex structure: Traditional electro-optic modulators require complex RF driving and bias circuits.
1.2 Environmental sensitivity: Sensitive to temperature and stress changes, prone to polarization state abnormalities.
1.3 Residual amplitude modulation (RAM) effect: This causes the DC bias of the error signal, leading to the drift of the laser locking point and seriously affecting the long-term stability of the system.
2. The innovative solution proposed by the research team is:
Completely abandon the traditional electro-optic modulator and adopt a collaborative design of semiconductor optical amplifier (SOA amplifier) combined with dual-path acousto-optic frequency shifters. The specific working principle is: After splitting the seed laser, it is precisely frequency-shifted by two dual-path acousto-optic frequency shifters, generating a frequency difference, and then the two paths of light are combined and injected into the SOA amplifier in the gain saturation state. By utilizing the nonlinear effects such as four-wave mixing (FWM) of the SOA amplifier, the multi-sideband signals required for PDH frequency locking are efficiently generated.
3. This technology brings the following disruptive performance advantages:
3.1 Overcoming the RAM problem and achieving ultra-high long-term stability: The SOA amplifier device (usually in a butterfly package) integrates temperature control and is extremely insensitive to environmental disturbances, avoiding the RAM problem from the physical mechanism and achieving cavity length locking accuracy better than 5×10⁻¹¹/day.
3.2 Precise matching of sidebands, significant improvement in signal-to-noise ratio: By independently controlling the shift amount of the two dual-path acousto-optic frequency shifters (100 MHz – 200 MHz) by two voltage-controlled oscillators (VCO), the frequency interval of the generated sidebands can be perfectly matched with the free spectral range (FSR) of the reference cavity, thereby greatly improving the signal-to-noise ratio of the error signal.
3.3 Cost reduction and efficiency improvement, conducive to system miniaturization: Without the expensive electro-optic modulator and complex circuits, the SOA optical amplifier only requires simple current drive, making the entire system more compact, lower in cost, and more suitable for high-precision laser external field applications and miniaturization.
3.4 The broad application prospects and market demand of this technology include:
Space and vehicle optical clocks: Its anti-disturbance characteristics perfectly meet the requirements of aerospace and unmanned vehicle fields.
Quantum gravimeters and cold atomic interferometers: Can be used for high-precision geological exploration and underwater navigation.
High-order fiber sensing and coherent phased array radar (LiDAR): Can provide extremely narrow linewidth, drift-free reference light sources.
Under the trend of the second global quantum revolution and miniaturization of quantum sensors, the market demand for autonomous controllable, low-cost, and stable frequency-stabilized laser module modules has sharply increased, and this patent technology precisely meets this market trend.