Optoelectronic Oscillator Jitter Reduction via Optical Feedback
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Solution Overview
Problem
Current optoelectronic oscillators face challenges in generating low-jitter optical and electrical signals in the GHz range due to high noise and high-frequency requirements, which increase costs and limit repetition rates, especially in passive mode-locking where stochastic emission leads to fluctuations, and active components are needed for electrical feedback, limiting performance.
Innovation Solution
An optoelectronic oscillator with a monolithically integrated passively mode-locked semiconductor laser and an optical feedback loop is designed, where the feedback loop's attenuation is set between 27.5 and 37.5 dB, and the time offset is adjusted so that feedback pulses arrive within the half-value width of original pulses, allowing 6000 to 7000 optical pulses to circulate, resulting in significantly reduced jitter values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive mode-locking is used to generate optical pulses, then the system operates at low cost without external high-frequency signals, but the stochastic nature of spontaneous emission leads to large fluctuations in pulse spacing and amplitude (high jitter)
Solution Approach 1:
The patent introduces optical feedback by feeding back a portion of the laser output through an optical delay line into the laser cavity. This feedback mechanism stabilizes the pulse train by reducing timing jitter and phase noise while maintaining the passive mode-locking operation, thus resolving the contradiction between low cost and high reliability
Solution Approach 2:
The patent replaces the need for external electrical high-frequency signals (electrical feedback system) with an optical feedback system using an optical delay line. This substitution maintains the low-cost advantage of passive mode-locking while achieving the jitter reduction normally requiring complex electrical feedback systems
2Reliability
If hybrid mode-locking with external high-frequency voltage signal is used to reduce phase noise, then the pulse train phase noise is decisively reduced, but high-frequency and low-noise electrical signals are essential and electrical power must be large (≥ 14 dBm), driving up costs
Solution Approach 1:
The patent substitutes the electrical feedback system (requiring high-power amplifiers and external signal sources) with an optical feedback system. The optical delay line provides the necessary phase noise reduction without requiring external high-frequency electrical signals, thereby maintaining low costs while achieving high reliability
Solution Approach 2:
The optical feedback system uses a portion of the laser's own output as the feedback signal, eliminating the need for external signal sources and power amplifiers. This self-service approach reduces complexity and cost while maintaining the phase noise reduction benefit
3Reliability
If optoelectronic oscillators with electrical feedback are used to generate low-jitter signals, then electrical signals with frequencies between 10 GHz and 100 GHz can be generated, but active components are required which limit the maximum repetition rate and increase production costs
Solution Approach 1:
The patent replaces the complex electrical feedback system with an optical feedback system using an optical delay line. This substitution eliminates the need for active electronic components such as amplifiers and modulators, thereby reducing device complexity while maintaining signal stability and enabling higher repetition rates
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 configuration achieves integrated jitter values of 219 femtoseconds or less, a five-fold reduction compared to previous oscillators, and allows for the simultaneous generation of low-noise optical and electrical signals without the need for external high-frequency signals, reducing costs and increasing repetition rates.
Implementation Method 1
an optical feedback loop which guides part of the optical radiation of the semiconductor laser and feeds it back into the semiconductor laser as feedback pulses
Implementation Method 2
The photons generated in the gain section, which are absorbed in this absorber section, excite an electron-hole pair. Since fewer states are available for further absorption processes for a short time, the absorption probability decreases. The absorber can therefore be saturated via photon absorption and becomes transparent
Implementation Method 3
The excited electron-hole pairs are now separated by the reverse voltage applied. After a certain time, the recovery time of the absorber, these states are available again for further absorption processes. The photocurrent generated by the separated electron-hole pairs, if it is modulated, leads to a modulation of the electrical resistance of the absorber section
Implementation Method 4
The coupling of the amplification in the gain section with the saturable absorption leads to the formation of pulses in the cavity via the process of mode coupling
Implementation Method 5
the attenuation of the feedback loop is between 27.5 and 37.5 dB and the time offset of the feedback loop is selected in such a way that each feedback pulse is generated within the time half-value width of a subsequent original pulse... resulting in significantly reduced jitter values
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 2(c)
AI summary
The invention relates, inter alia, to an optoelectronic oscillator (10) for generating an optical and/or electric pulse comb, comprising a monolithically integrated passively mode-coupled semiconductor laser (20) and an optical feedback loop (80) which guides a part of the optical radiation of the semiconductor laser (20) and feeds said part back into the semiconductor laser (20) as feedback pulses (Pr). Without the influence of the feedback pulses (Pr), the semiconductor laser (20) would emit comb-like optical pulses, hereafter referred to as primary pulses, and in the event of an influence, emits comb-like output pulses (Pa) which have been influenced by the feedback pulses (Pr), said output pulses having a lower temporal jitter or less phase noise than the primary pulses. According to the invention, the feedback loop (80) is damped between 27.5 and 37.5 dB, and the time lag of the feedback loop (80) is selected such that each feedback pulse (Pr) is incident within the temporal half-value width of each subsequent primary pulse, i.e. the next pulse which the semiconductor laser (20) would have generated without being influenced by the incident feedback pulse (Pr).