This work was supported by the National Natural Science Foundation of China (NSFC) (Grant 62075238, 61675231) and&#160;the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB24030600).

1. Optical coupling
<ol>
	<li>Polish the end-face of the MRR on a grinding plate using 1.5 &#956;m abrasive powders (aluminum oxide) mixed with water for 5 min.</li>
	<li>Fix the MRR with a chip fixture and place an eight-channel FA on a six-axis coupling stage, which includes three linear stages with a resolution of 50 nm and three angle stages with a resolution of 0.003&#176;. The patches of the MRR and FA are 250 &#956;m.</li>
	<li>Use a 1,550 nm laser as an optical source for real-time monitoring of the coupling ef...

<ol>
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On-chip DKSs provide novel compact coherent optical sources and exhibit excellent application prospects in optical metrology, molecular spectroscopy, and other functions. For commercial applications, compact packaged micro-comb sources are essential. This protocol provides a practical approach to make a packaged micro-comb that benefits from the reliable, low coupling loss connection between the MRR and FA, as well as a robust thermal-controlled DKS generation method. Therefore, our experiments are no longer coupling sta...

The steady DKSs in microresonators, where the cavity dispersion is balanced by Kerr nonlinearity, as well as the Kerr gain and cavity dissipation1, have attracted great interest in the scientific research community for their ultra-high repetition rate, compact size, and low cost2. In the time domain, DKSs are stable pulse trains that have been used for high-speed ranging measurement3 and molecular spectroscopy4. In the frequency domain, DKSs have a series of frequency lines with equal frequency spacing that are suitable for wavelength-division-multiplex (WDM) communications systems5,6, optical frequency synthesis7,8, and ultra-low noise microwave generation9,10, etc. The phase noise or linewidth of comb lines directly affects the performance of these application systems. It has been proven that all the comb lines have a similar linewidth with the pump11. Therefore, using an ultra-narrow linewidth laser as a pump is an effective approach to improve the performance of DKSs. However, the pumps of most reported DKSs are frequency sweeping external cavity diode lasers (ECDLs), which suffer from relatively high noise and have a broad linewidth on the order of tens to hundreds of kHz. Compared with tunable lasers, fixed-frequency lasers have less noise, narrower linewidths&#160;and smaller volume. For example, Menlo systems can provide ultra-stable laser products with a linewidth of less than 1 Hz. Using such a frequency fixed laser as a pump can significantly reduce the noise of the generated DKSs. Recently, microheater or thermoelectric cooler (TEC)-based thermal tuning methods have been used for DKSs generation12,13,14.
Repetition rate stability is another important parameter of DKSs. Generally, frequency counters are used to characterize the frequency stability of DKSs within a gate time, which is generally on the order of a microsecond to a thousand seconds15,16. Limited by the bandwidth of the photodetector and frequency counter, electro-optic modulators or reference lasers are typically used to lower the detected frequency when the free-spectral-range (FSR) of the DKSs is over 100 GHz. This not only increases the complexity of test systems, but also produces additional measurement errors caused by the stability of RF sources or reference lasers.
In this paper, a micro-ring resonator (MRR) is butterfly packaged with a commercial TEC chip that is used to control the operation temperature. Using a frequency fixed laser with a linewidth of 100 Hz as a pump, soliton crystals (SCs) are stably generated by manually decreasing the operating temperature; these are special DKSs that can completely fill a resonator with collectively ordered ensembles of copropagating solitons17. To the best of our knowledge, this is the narrowest linewidth pump in DKSs generation experiments. The power spectral density (PSD) spectrum of every comb line is measured based on a delayed self-heterodyne interferometer (DSHI) method. Benefitting from the ultra-narrow linewidth of the comb lines, the repetition rate instability of soliton crystals (SCs) is derived from the central frequency drift of the PSD curves. For the SC with a single vacancy, we obtained a repetition rate instability of ~53.24 Hz within 10 &#181;s and ~509.32 Hz within 125 &#181;s.
The protocol consists of several main stages: First, the MRR is coupled with a fiber array (FA) using a six-axis coupling stage. The MRR is fabricated by a high-index doped silica glass platform18,19. Then, the MRR is packaged into a 14-pin butterfly package, which increases the stability for the experiments. SCs are generated using a thermal-controlled method. Finally, the repetition rate fluctuations of SCs are measured by a DSHI method.

<table border="0" cellpadding="0" cellspacing="0" style="width:1421px;" width="1421">
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		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:299px;">6-axis coupling stage</td>
			<td style="width:323px;">Suruga Seiki</td>
			<td style="width:161px;">KXC620G 
			KGW060</td>
			<td style="width:639px;">Contains 3 linear motorized translation states and 3 angular motorized rotational stages. 
			Linear state: Minimum stepping: 0.05 &#956;m; Travel: 20mm; Max.speed: 25mm/s; Repeatability: +/-0.3 &#956;m; Rotational stage:Travel: &#177;8&#176;; Resolution/pulse: 0.003 degree; Repeatability:&#177;0.005&#176;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Abrasive powder</td>
			<td style="width:323px;">Shenyang Kejing Auto-Instrument Co., LTD</td>
			<td>2980002</td>
			<td>Silicon carbide, granularity: 1.5 &#956;m</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:299px;">Glue 3410</td>
			<td style="width:323px;">Electronic Materials Incorporated</td>
			<td style="width:161px;">Optocast 3410</td>
			<td style="width:639px;">Optocast 3410 is an ultra violet light and heat curable epoxy suitable for opto-electronic assembly. It cures rapidly when exposed to U.V. light in the 320-380 nm.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:299px;">High-index doped silica glass</td>
			<td style="width:323px;">Home-made</td>
			<td style="width:161px;">-</td>
			<td style="width:639px;">The MRR is fabricated by a high index doped silica glass platform. The waveguide section is 2&#215;3 &#956;m and radius is 592.1 &#956;m, corresponding to FSR of 49 GHz.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Pump laser</td>
			<td style="width:323px;">NKT Photonics</td>
			<td style="width:161px;">E15</td>
			<td style="width:639px;">It is a continuous wave fiber laser with linewidth of 100 Hz.</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:299px;">Ultrastable Laser</td>
			<td style="width:323px;">Menlosystems</td>
			<td style="width:161px;">ORS</td>
			<td>State-of-the-art linewidth (&#60;1Hz) and stability (&#60;2 x 10-15 Hz)</td>
		</tr>
	</tbody>
</table>

rapid repetition rate fluctuation measurement of soliton crystals in a microresonator

Temporal solitons have attracted great interest in the past decades for their behavior in a steady state, where the dispersion is balanced by the nonlinearity in a propagation Kerr medium. The development of dissipative Kerr solitons (DKSs) in high-Q microcavities drives a novel, compact, chip-scale soliton source. When DKSs serve as femtosecond pulses, the repetition rate fluctuation can be applied to ultrahigh precision metrology, high-speed optical sampling, and optical clocks, etc. In this paper, the rapid repetition rate fluctuation of soliton crystals (SCs), a special state of DKSs where particle-like solitons are tightly packed and fully occupy a resonator, is measured based on the well-known delayed self-heterodyne method. The SCs are generated using a thermal-controlled method. The pump is a frequency fixed laser with a linewidth of 100 Hz. The integral time in frequency fluctuation measurements is controlled by the length of the delay fiber. For a SC with a single vacancy, the repetition rate fluctuations are ~53.24 Hz within 10 &#181;s and ~509.32 Hz within 125 &#181;s, respectively.

Figure 3 shows the transmission power trace while a resonance thermal was tuned across the pump. There was an obvious power step that indicated the generation of SCs. The step had similar power compared with its precursor, the modulational instability comb. Therefore, the generation of SCs was not tuning speed dependent. The SCs exhibited a great variety of states, including vacancies (Schottky defects), Frenkel defects, and superstructure12,<sup class="xre...

Watch this Scientific Journal Video about Rapid Repetition Rate Fluctuation Measurement of Soliton Crystals in a Microresonator at JoVE.com

Rapid Repetition Rate Fluctuation Measurement of Soliton Crystals in a Microresonator

Here, we present a protocol to generate soliton crystals in a butterfly-packaged micro-ring resonator using a thermal tuned method. Further, the repetition rate fluctuations of a soliton crystal with a single vacancy are measured using a delayed self-heterodyne method.

Temporal solitons have attracted great interest in the past decades for their behavior in a steady state, where the dispersion is balanced by the ...

Recent years, dissipative Kerr soliton has become a novel chip-scale coherent light source, which has attracted great attention for the enormous value in soliton physics research and practical applications. Dissipative Kerr soliton has high repetition rate. So it is a challenge to measure the relative parameters, especially the repetition rate fluctuation.In our work, we figure out a way to get it. Meanwhile, a robust package is necessary for practical applications. Our protocol provides an effective method for on-chip micro-ring resonator packaging, soliton generation, and measurement of repetition rate fluctuation.To begin, fix the micro-ring resonator with a chip fixture. On a six axis coupling stage, which includes three linear stages with a resolution of 50 nanometers and three angle stages with a resolution of 0.003 degrees, place an eight channel fiber array. Use a 1, 550 nanometer laser as an optical source for real-time monitoring of the coupling efficiency.Carefully adjust the position of the fiber array. Measure the input power and output power by an optical power meter. Keep the inset loss at the minimum value, typically less than six decibels, corresponding to a coupling loss of less than three decibels per facet.Use an ultraviolet curved adhesive to glue the micro-ring resonator and fiber array. Place the adhesive on the side edge of the contacting surface to ensure that there is no glue on the optical path. Expose the UV curved adhesive to a UV lamp for 150 seconds and bake in a chamber at 120 degrees Celsius for more than one hour.Co agglutinate a 10.2 millimeter by 6.05 millimeter thermal electric cooler chip with a maximum power of 3.9 Watts to the base plate of a standard 14 pin butterfly package using silver glue. Sauter the two electrodes of the thermoelectric cooler chip to two pins of the butterfly package. Paste a tungsten plate to the surface of the thermal electric cooler chip using silver glue.Use the tungsten plate as a heat sink to fill the gap between the thermal electric cooler and the micro-ring resonator. Use an erbium doped fiber amplifier to boost the pump for micro comb generation. Control the polarization state of the pump using a fiber polarization controller.Connect all the devices using single mode fibers. Fix the wavelength of the pump laser. At 1556.3 nanometers, manually tune the operation temperature through an external commercial thermoelectric cooler controller to above 66 degrees Celsius, which is high enough to move a resonance of the micro-ring resonator to the top of the tungsten plate using silver glue, and fix the pigtail of the fiber array to the output board of the butterfly package to the red side of the pump.Monitor the output optical spectrum with an optical spectrum analyzer. Detect the output power trace with a three gigahertz photo detector and record with an oscilloscope. Set the output of the erbium doped fiber amplifier to 34 decibel milliwatts, or responding to an on-chip power of 30.5 decibel milliwatts, which ensures that there is enough power coupled into the micro-ring resonator for micro comb generation.Set the thermistor to two kilohms corresponding to an operating temperature of 66 degrees Celsius, then slowly decrease the operating temperature by increasing the set value of the thermistor. Tune the polarization of the pump by the fiber polarization controller, until a soliton crystal's step is observed at the falling edge of the triangular transmission power trace. When a palm like optical spectrum is observed on the optical spectrum analyzer, stop decreasing the operation temperature.The value of the thermistor was around at 5.6 kilohms in these experiments. Connect the generated soliton crystals to a tuneable band pass filter to extract an individual comb line. Set the pass band of the tuneable band pass filter to 0.1 nanometers.Tune its central wavelength over the full C and L band, and set the filter slope to 400 decibels per nanometer. Couple of the selected comb line to an asymmetric mock Zehnder interferometer. Use an acousto-optic modulator to shift the optical frequency in one arm of the asymmetric mock sender interferometer by 200 megahertz.The optical field in the other arm is delayed by a segment of optical fibers of two kilometers and 25 kilometers. Attach a photodiode to detect the output optical signal and use an electrical spectrum analyzer to analyze the power spectral density spectrum. Tune the central wavelength of the tuneable band pass filter.Measure the power spectral densities of every comb line. Using same method, measure the power spectral density curves of soliton crystals with a vacancy. Record the three decibel bandwidth of the power spectral density curve, and that'll enter your fit to it piecewise through a Python program.This figure shows the transmission powertrains while a resonance thermal was tuned across the pump. There was an obvious power step that indicated the generation of soliton crystals. A perfect soliton crystal with 27 solitons is shown here, as well as a soliton crystal with a single vacancy.The perfect soliton crystals based on a two kilometer and a 25 kilometer delay fiber were observed with power spectral density curves having flat tops, which were caused by the frequency fluctuation within the delay time. The typical optical spectrum of soliton crystals based on a two kilometer and a 25 kilometer delay fiber were fitted piecewise with linear lines plotted in blue. In summary, an on-chip micro-ring resonator is packed in a butterfly cell and a thermal tuning method is proposed generate soliton crystal.Finally, we use delayed self-heterodyne method to achieve the measurement of the repetition rate fluctuation.

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2.9K visualizações.  Chinese Academy of Sciences (CAS). Nos últimos anos, o dissipativo Kerr soliton tornou-se uma nova fonte de luz coerente em escala de chip, que tem atraído grande atenção pelo enorme valor na pesquisa de física de soliton e aplicações práticas. Dissipativo Kerr soliton tem alta taxa de repetição. Portanto, é um desafio medir os parâmetros relativos, especialmente a flutuação da taxa de repetição.Em nosso trabalho, descobrimos uma maneira de obtê-lo. Enquanto isso, um pacote robusto é necessário para a...