A Novel Symmetric Dual Loop Feedback Scheme Insensitive to Phase Tuning Using Self-Mode-Locked Two-Section Quantum Dash Laser (original) (raw)
Related papers
Stabilization of self-mode-locked quantum dash lasers by symmetric dual-loop optical feedback
2018
We report experimental studies of the influence of symmetric dual-loop optical feedback on the RF linewidth and timing jitter of self-mode-locked two-section quantum dash lasers emitting at 1550 nm. Various feedback schemes were investigated and optimum levels determined for narrowest RF linewidth and low timing jitter, for single-loop and symmetric dual-loop feedback. Two symmetric dual-loop configurations, with balanced and unbalanced feedback ratios, were studied. We demonstrate that unbalanced symmetric dual loop feedback, with the inner cavity resonant and fine delay tuning of the outer loop, gives the narrowest RF linewidth and reduced timing jitter over a wide range of delay, unlike single and balanced symmetric dual-loop configurations. This configuration with feedback lengths of 80 and 140 m narrows the RF linewidth by ∼ 4-67x and ∼ 10-100x, respectively, across the widest delay range, compared to free-running. For symmetric dual-loop feedback, the influence of different power split ratios through the feedback loops was determined. Our results show that symmetric dual-loop feedback is markedly more effective than single-loop feedback in reducing RF linewidth and timing jitter, and is much less sensitive to delay phase, making this technique ideal for applications where robustness and alignment tolerance are essential.
Optimum Stabilization of Self-Mode-Locked Quantum Dash Lasers Using Dual Loop Optical Feedback
IEEE , 2017
We have experimentally investigated the RF linewidth and timing jitter in self-mode-locked two-section quantum dash lasers emitting at ~1.55 µm and operating at ~21 GHz repetition rate, subjected to single and dual loop optical feedback into the gain section, over a wide range of feedback delay. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual-loop configurations. We demonstrate that dual-loop feedback with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, 10 – 50× better than single-loop feedback. In addition, for dual-loop configurations, under fully resonant conditions, phase noise is reduced to 295 fs [10 kHz – 100 MHz], the RF linewidth narrows to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual-loop optical feedback with separate fine tuning of both external cavities is far superior to single-loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.
IEEE Photonics Journal, 2020
In the present work, we report a path of RF stabilization versus delay subject to self-mode-locked (SML) two-section quantum-dash (QDash) lasers emitting at ∼1.55 μm and operating at ∼21 GHz repetition rate using a feedback ratio controlled and optical delay phase-dependent symmetric dual-loop optical feedback. For symmetric dual-loops (equal arms of external loops), we identify the three key parameters: power-split ratio through each cavity of the external feedback loop, optical delay phase settings, and overall feedback strength back into gain section, yields jitter stabilization on integer resonance as well as on full delay range tuning. Symmetric dual-loop feedback with two optical delay phase settings (weaker cavity set to integer resonance, fine-tuning of the stronger cavity and stronger cavity set to integer resonance, fine-tuning of a weaker cavity) and four chosen combinations of feedback ratios (−19.5:−29.03 dB, −20.6:−24.3 dB, −21:−22.7 dB, −21.3:−23 dB) has been demonstrated. Based on these four chosen combinations of feedback ratios and optical delay phase settings, a path of stabilization has been identified for SML QDash lasers using symmetric dual-loop optical feedback. Our proposed dual-loop feedback schemes provide a viable path towards the stabilization of mode-locked lasers, promising for various practical applications where ultra-stable optical pulses are highly desirable.
Optics Express, 2017
We experimentally investigate the RF linewidth and timing jitter over a wide range of delay tuning in a self-mode-locked two-section quantum dash lasers emitting at~1.55µm and operating at~21 GHz repetition rate subject to single and dual optical feedback into gain section. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual loop configurations. We demonstrate that dual loop feedback, with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, unlike single loop feedback. In addition, for dual loop configurations, under fully resonant conditions, integrated timing jitter is reduced from 3.9 ps to 295 fs [10 kHz-100 MHz], the RF linewidth narrows from 100 kHz to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual loop optical feedback with separate fine tuning of both external cavities is far superior to single loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.
arXiv, 2017
We investigate the influence of symmetric dual-loop feedback (loops with equal length) as a function of full delay tuning on the RF linewidth and timing stability of ~ 21 GHz self-mode-locked quantum dash laser. Various feedback scenarios are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both feedback schemes. Two symmetric dual-loop configurations, subject to balanced (equal feedback strength through either feedback cavity) and unbalanced feedback ratio (~ 4x more power through loop-I relative to other) are presented here. We demonstrated that unbalanced symmetric dual-loop, with the inner cavity fully resonant (at higher feedback intensity) and fine delay tuning of the outer loop (at lower feedback intensity), gives narrow RF linewidth and reduced timing jitter over a wide range of delay detuning, unlike single and balanced symmetric dual-loop configurations. This study reveals that unbalanced symmetric dual-loop with feedback delay lengths 80 and 140 m narrows the RF linewidth by ~ 4-67x (~ 2-9x timing jitter reduction) and ~ 10-100x (~ 2.5-10x timing jitter reduction), respectively, across the widest delay range, compared to free-running condition. The influence of symmetric dual-loop with balanced and unbalanced feedback ratio on the stability of the laser device is further discussed. These results suggests that symmetric dual-loop feedback with controlled feedback strength over each loop and without additional delay time in external feedback loops is significantly more effective than single loop feedback in reducing RF linewidth and timing jitter, across full range of delay phase tuning. Wider resonant feedback regime as a function of full delay tuning achieved with symmetric dual-loop configuration makes this technique ideal for practical applications where robustness and tolerance to misalignment are essential.
Opt. Express 25, 15796-15805 (2017)
We experimentally investigate the RF linewidth and timing jitter over a wide range of delay tuning in a self-mode-locked two-section quantum dash lasers emitting at ~ 1.55µm and operating at ~ 21 GHz repetition rate subject to single and dual optical feedback into gain section. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual loop configurations. We demonstrate that dual loop feedback, with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, unlike single loop feedback. In addition, for dual loop configurations, under fully resonant conditions, integrated timing jitter is reduced from 3.9 ps to 295 fs [10 kHz-100 MHz], the RF linewidth narrows from 100 kHz to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual loop optical feedback with separate fine tuning of both external cavities is far superior to single loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.
Optics and Laser Technology, 2020
This paper reports the effectiveness of a variety of single-and dual-loop optical feedback arrangements on stability of self-mode-locked two-section quantum dash lasers emitting at ≈1.55 µm and operating at 21 GHz repetition rate. We describe reduction of RF linewidth and timing jitter using five distinct schemes, including single and dual loops with symmetric and asymmetric lengths, and with balanced and unbalanced feedback ratios. All feedback schemes described are effective in stabilizing the pulse trains from SML QDash lasers, but some require precisely tuned resonance between loop delay and laser cavity. We show balanced asymmetric dual-loop optical feedback is the most robust, cost-effective and low-noise method to stabilize and control pulses from mode-locked lasers and optoelectronic oscillators.
Optics Letters, 2017
We demonstrate an asymmetric dual-loop feedback method to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single-and dual-loop feedback. In this Letter, we report optimal suppression of spurious tones by optimizing the delay in the second loop. We observed that asymmetric dual-loop feedback, with large (∼8×) disparity in loop lengths, gives significant suppression in external-cavity side-modes and produces flat radio frequency (RF) spectra close to the main peak with a low timing jitter, compared to single-loop feedback. Significant reduction in RF linewidth and timing jitter was produced by optimizing the delay time in the second feedback loop. Experimental results based on this feedback configuration validate predictions of recently published numerical simulations. This asymmetric dual-loop feedback scheme provides simple, efficient, and cost-effective stabilization of optoelectronic oscillators based on mode-locked lasers. Semiconductor mode-locked diode lasers (MLLs) are compact, rugged, and efficient sources of ultra-short, intense, and high-repetition frequency optical pulses with many potential applications such as all-optical clock recovery, lidar, optical frequency combs, and telecommunications [1-3]. A major limitation of MLLs for most practical applications is their very high timing jitter and phase noise, as spontaneous emission noise and cavity losses make MLLs prone to broad linewidths and, therefore, substantial phase noise [4]. To improve the timing jitter, several experimental methods such as single-cavity feedback [5-8], coupled optoelectronic oscillators [9], injection locking [10-12], and dual-loop feedback [13-15] have been proposed and demonstrated. Of the stabilization techniques demonstrated to date, optical feedback is a promising approach in which an additional reflector creates a compound cavity with a high quality factor, with no need for an external radio frequency (RF) or optical source. Due to the existence of the extra mirror, sidebands resonant with the round-trip time of the external cavity are generated which affect the overall timing jitter and quality of the RF spectra. To overcome these issues, optoelectronic feedback [9] can also be utilized to stabilize the timing jitter and to suppress cavity side-modes by conversion of the optical oscillation (using a fast photodetector) to an electrical signal used in a long feedback loop. This technique does not require an RF source, but requires optical-to-electrical conversion. Recently, a simpler dual-loop feedback technique [13-15] without optical/electrical conversion has been demonstrated to improve timing jitter of the MLLs and to filter or suppress the unwanted spurious side-bands. Dual-loop configuration proposed to date [13,14] yields a sub-kilohertz line-width, but produces additional noise peaks at frequencies resonant with the inverse of the delay time in the second cavity. This is undesirable in many applications where low noise and flat spectra are required, as in frequency comb generation. Most recently, the influence of the second feedback delay on side-mode suppression [16] and timing jitter [17] has been studied numerically. In this Letter, we report experimental investigation to eliminate these adverse dynamical effects using asymmetric dual-loop feedback by appropriately choosing the length of the second feedback cavity. The best side-mode suppression and lower timing jitter relative to single-loop feedback were achieved with the length ratio between the two cavities ∼8×. It was further observed that the RF linewidth and integrated timing jitter were reduced by increasing the length of the second cavity. Our findings suggest that noise stabilization and side-mode suppression depend strongly on additional feedback delay times. Devices under investigation are two-section InAs/InP quantum dash mode-locked laser (QDash MLL) with an active layer composed of nine InAs quantum-dash monolayers grown by gas source molecular beam epitaxy embedded within two barriers and separate confinement heterostructure (SCH) layers (dash in a barrier structure). Both barriers and SCH layers consisted of In 0.8 Ga 0.2 As 0.4 P 0.6 quaternary materials with 3714 Vol. 42, No. 18 / September 15 2017 / Optics Letters Letter 0146-9592/17/183714-04 Journal
Applied Optics, 2018
In this paper, we report stabilization of self-mode-locked two-section quantum-dash lasers on the widest range of delay using simultaneous optical injection and optical feedback. With continuous-wave optical injection, various wavelengths spanning a range from 1568 to 1578 nm were investigated and optimum wavelengths (1571.210 to 1572.710) yielding the narrowest RF linewidth and reduced timing jitter of slave laser were identified. In addition, the dependence of RF linewidth and pulse repetition rate on injected wavelength was further explored. Our results indicate that simultaneous optical feedback and optical injection significantly improves the RF linewidth across the widest delay range compared to optical feedback alone. Under fully resonant feedback and optimum injection parameters, a minimum RF linewidth of 1 kHz (instrument limited) was achieved with simultaneous optical injection plus optical feedback, which was >2× lower than optical feedback alone and more than 100× lower than free-running. This stabilization technique is implemented in an all-optical arrangement without optical/ electrical conversion, which is ideal for high-repetition-rate devices and photonic integration.
Photonics
We report feedback-induced frequency oscillations using a power-split-ratio through asymmetric dual-loop optical feedback (Loop I: ~2.2 km and Loop II: ~20 m) subject to a self-mode-locked two-section QDash laser emitting at 1550 nm and operating at 21 GHz repetition rate. To assess the suppression of frequency resonances, three chosen combinations of feedback power (Loop I: −27.27 dB and Loop II: −19.74 dB, Loop I: −22 dB and Loop II: −22 dB, and Loop I: −19.74 dB and Loop II: −27.27 dB) through asymmetric dual-loop optical feedback have been studied. Based on the chosen coupling strength, an optimum feedback ratio that yields better side-mode suppression has been identified. Our results demonstrate that side-mode suppression can be achieved by the fine adjustment of coupling power through either cavity of dual-loop feedback configurations. Furthermore, we have further demonstrated that frequency fluctuations from the RF spectra can be filtered by carefully selecting the delay phas...