Laser Frequency Noise Cancellation Using Cavity Feedforward Control
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Solution Overview
Problem
Existing laser technologies face challenges in achieving long-term frequency stability and suppressing fast-frequency noise, particularly in applications like quantum computing and atomic clocks, where high-finesse optical cavities can introduce undesirable constraints and limitations.
Innovation Solution
The implementation of a device that uses an optical cavity to filter out high-frequency noise from a laser output, generating a modified signal which is then used to create a beat note with the laser output to derive a frequency error signal for real-time frequency correction via an electro-optic modulator, incorporating signal delay compensation to achieve noise suppression beyond the servo bump frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-finesse optical cavity is used to filter laser frequency noise, then long-term frequency stability is improved, but the system design becomes constrained and servo bumps are introduced at high frequencies
Solution Approach 1:
The patent divides the laser output into two separate paths: one path passes through the optical cavity for frequency stabilization while the other path remains unfiltered. This segmentation allows the system to maintain long-term stability through the cavity-stabilized path while preserving fast-frequency components in the unfiltered path, thereby avoiding the servo bump problem and reducing design constraints.
2Reliability
If feedback control is used to stabilize laser frequency, then frequency stability is improved, but fast-frequency noise is pushed to high frequencies creating servo bumps
Solution Approach 1:
Instead of using conventional feedback control that pushes noise to high frequencies, the patent inverts the approach by using feedforward control. The unfiltered laser signal is used to predict and cancel noise in the filtered signal before it affects the quantum system, thereby stabilizing frequency without creating harmful servo bumps.
3Object-affected harmful factors
If the laser output is fully filtered through the optical cavity, then frequency noise is suppressed, but signal delay and loss increase
Solution Approach 1:
The patent applies partial filtering by using only a portion of the laser output through the optical cavity. The feedforward signal is derived from the unfiltered portion, which experiences no delay or loss, and is then used to correct the filtered portion. This partial action approach suppresses noise while minimizing signal delay and loss.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in at least 20 dB noise suppression at the peak of the servo bump and a noise suppression bandwidth of about 5 MHz, maintaining long-term stability while being compatible with commercial systems and applicable to emerging laser applications, including cold atom systems.
Implementation Method 1
an optical cavity exhibiting a resonant optical frequency
Implementation Method 2
an acousto-optic modulator configured to interfere a second portion of the laser output with a first portion of the modified signal at a beat frequency
Implementation Method 3
an acousto-optic modulator configured to interfere
Implementation Method 4
an electro-optic modulator configured to interfere a second portion of the reference signal with a second portion of the modified signal using the feedforward signal
Data Source
AI summary
The present disclosure relates to active cancellation of frequency noise in lasers. One example embodiment includes a device. The device includes an optical cavity exhibiting a resonant optical frequency. The device also includes a laser. An output of the laser is locked to the resonant optical frequency. A first portion of the laser output is transmitted through the optical cavity to filter out high-frequency noise from the first portion of the laser output to generate a modified signal. Additionally, the device includes an acousto-optic modulator configured to generate a reference signal. Further, the device includes a feedforward circuit configured to receive a first portion of the reference signal and generate a feedforward signal. In addition, the device includes an electro-optic modulator configured to interfere a second portion of the reference signal with a second portion of the modified signal using the feedforward signal to generate an output signal.