Review on Methods for Laser Linewidth Measurement

Mingbin Cui; Jungang Huang; Xiulun Yang

doi:10.3788/LOP202158.0900005

Laser & Optoelectronics Progress, Volume. 58, Issue 9, 0900005(2021)

Review on Methods for Laser Linewidth Measurement

Mingbin Cui¹, Jungang Huang², and Xiulun Yang^1、*

Author Affiliations

¹School of Information Science and Engineering, Shandong University, Qingdao , Shandong 266237, China

²Guangdong Raying Laser Technology Co. Ltd., Dongguan , Guangdong 523808, China

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Abstract Get PDF(in Chinese)

Figures & Tables(25)

Fig. 1. Relationship among beat frequency signals processed by different methods

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Fig. 2. System principle diagram of double beam heterodyne method

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Fig. 3. Experimental device for linewidth measurement ^[16]

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Fig. 4. Principle structural diagram of delayed self-zero heterodyne method

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Fig. 5. Delayed nonzero self-heterodyne method based on Mach-Zehnder interferometer

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Fig. 6. Principle structural diagram of delayed self-heterodyne method based on Michelson interferometer

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Fig. 7. Principle structural diagram of delayed self-heterodyne method with cyclic gain compensation ^[19]

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Fig. 8. Cyclic auto-heterodyne linewidth measurement system based on Michelson interferometer^[22]

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Fig. 9. Experimental structural diagram ^[24]

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Fig. 10. Schematic of experimental device ^[28]

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Fig. 11. Principle diagram of experimental device ^[31]

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Fig. 12. Delayed fiber lengths and corresponding $Δ S$ for different prediction linewidths^[31]

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Fig. 13. Principle diagram of laser linewidth measurement^[32]

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Fig. 14. Relationship between prediction linewidth and $k$ ^[33]. (a) $k < 10$ ; (b) $k < 0.1$

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Fig. 15. Principle structural diagram of DSHI with second-order Stokes light as reference light^[34]

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Fig. 16. System structural diagram of cross correlation method for laser linewidth measurement ^[36]

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Fig. 17. Frequency noise distribution and β-separation line^[38]

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Fig. 18. Principle structural diagram of unbalanced optical fiber interferometer measurement method^[39]

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Fig. 19. Simulated $S_{L} (ω_{B}, τ_{d})$ power spectra ^[20]

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Fig. 20. Simulated $\frac{1}{f}$ noise spectra under different time delays^[52]

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Fig. 21. Voigt spectra under different Gaussian and Lorentz spectral widths ^[52]

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Fig. 22. Frequency variation caused by typical mechanical noise ^[10]

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Table 1. Linewidth relationship in DSHI linewidth measurement
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Table 1. Linewidth relationship in DSHI linewidth measurement
Measurement position /dB Full width of beat spectral line
-3 [2Δv]
-10 [2 $\sqrt[]{9}$ Δv]
-20 [2 $\sqrt[]{99}$ Δv]
-30 [2 $\sqrt[]{999}$ Δv]

Table 2. $Δ f$ and $Δ S$ for different predicted linewidth and delaying fiber lengths^[31]
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Table 2. $Δ f$ and $Δ S$ for different predicted linewidth and delaying fiber lengths^[31]
Δf_est（kHz） Delaying length (m) ΔS(dB) Δf(kHz)
0.1 5000 21.98 0.15
2.5 1000 17.11 2.30
10 500 14.31 9.10
20 300 13.50 18.20
150 50 12.98 125
450 15 12.78 430

Table 3. Summary and comparison of methods for linewidth measurement

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Table 3. Summary and comparison of methods for linewidth measurement

Method	Measurement accuracy	Advantage	Disadvantage
Double beam heterodyne method	Dependent only on reference light width^[11,16]	High frequency band, high resolution, high sensitivity	Need of reference laser with narrow linewidth close to measured laser frequency, two beat frequency beams continuously, stably and precisely controlled in a very small range, high requirements for experimental instruments and environment, narrow application range
Dynamic linewidth measurement technology based on digital coherent receiver	Dependent only on reference light width^[11,16]	Available measurement of both dynamic linewidth and static linewidth, obvious advantages in detecting tunable DSDBR laser linewidth and evaluating performance of tunable laser in high-speed coherent communication system	No obvious advantages in static line width measurement
Delayed self-zero heterodyne method^[57-59]	>1 kHz^[12,15,20]	No need of acousto-optic modulator, reduced cost, small loss of output optical power, increased sensitivity,being conducive to circuit integration	Near-zero-frequency operation, being easy to be affected by surrounding environment, not being easy to read line width directly
Delayed nonzero heterodyne method based on Mach- Zehnder interferometer^[40,60-62]		Being able to read both half height and full width of beat frequency signal intuitively, no need of high stability reference source	Long time delay optical fiber needed, Rayleigh scattering and loss introduced to bring inconvenience to measurement, high requirements for anti-interference ability of system, insertion loss introduced using acousto-optic frequency shifter
Delayed nonzero heterodyne method based on Michelson interferometer		Length of delayed optical fiber halved, Faraday rotating mirror (FRM) directly connected at reflection end ^[63-65]， independent of polarization, accuracy improved	More complex structure, fiber with large loss
Cyclic gain compensation delayed self-heterodyne method^[66]		Length of optical fiber and cost greatly reduced	Insertion loss introduced into acousto-optic frequency shifter, poor stability of polarization state in system, high optical loss
DSHI generated by Brillouin ring laser using second-order Stokes light as reference light	<100 kHz^[34]	Very small lower limit of laser measurement, high measurement accuracy, simple structure, less optical devices used , no need of long fiber, wide measurement band, and measurement not limited by pump light wavelength and in a wide spectral range	Being impossible to measure wide laser linewidth, being necessary to keep ambient temperature constant to ensure single longitudinal mode operation ^[67-68]
Ultra-narrow linewidth measurement based on Voigt profile fitting	>10 Hz^[24]	Spectral broadening effect by 1/f frequency noise and Lorentzian line shape from measured spectra ignored, high resolution	Complicated calculation
High-precision narrow laser linewidth measurement based on coherent envelope demodulation	>1 kHz^[28]	Gaussian broadening effect by 1/f frequency noise ignored	Complicated iterative process
Characterization of linewidth by autocorrelation detection using strong coherent envelope	>1 kHz^[31]	Short fiber length required, near center-frequency of CDSPST value, minimum detection error, high frequency stability, high accuracy	Inconvenience measurement due to polarization state and loss introduced by acousto-optic frequency shifter
Measurement method based on unbalanced optical fiber interferometer	>1 kHz^[39]	Simple structure of system, simple operation, no need of long delayed fiber, less application of acousto-optic modulator, high measurement accuracy, no need of Lorentz fitting	High requirement of interferometer for surrounding environment, being easy to introduce random errors, repeated measurements needed for average
Narrow-band laser linewidth measurement based on cross-correlation method and β algorithm	>20 Hz^[36]	Lot of system noise eliminated using cross-correlation principle, linewidth information more accurately captured, no need of Lorentz fitting, small experimental errors, linewidth of 2 μm band measured	Complex algorithm, associated noises in system not eliminated
Ultra-narrow linewidth measurement based on two parameter acquisition with partially coherent light interference	>100 Hz and <100 kHz^[32]	Influence of 1/f noise reduced using optical fiber with kilometer level long delay, no influence of fiber length, small measurement errors	Scattering loss and 1/f noise introduced by acousto-optic frequency shifter and time-delay fiber, which limiting improvement of measurement accuracy, not being suitable for wide linewidth measurement

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Mingbin Cui, Jungang Huang, Xiulun Yang. Review on Methods for Laser Linewidth Measurement[J]. Laser & Optoelectronics Progress, 2021, 58(9): 0900005

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Paper Information

Category: Reviews

Received: Sep. 2, 2020

Accepted: Sep. 22, 2020

Published Online: May. 12, 2021

The Author Email: Yang Xiulun (xlyang@sdu.edu.cn)

DOI:10.3788/LOP202158.0900005

Topics

laser devices and laser physics

Lasers and Laser Optics

Laser physics

laser manufacturing

Instrumentation, Measurement and Metrology

Table 1. Linewidth relationship in DSHI linewidth measurement

Table 1. Linewidth relationship in DSHI linewidth measurement

Table 2. Δf and ΔS for different predicted linewidth and delaying fiber lengths[31]

Table 2. Δf and ΔS for different predicted linewidth and delaying fiber lengths[31]

Table 3. Summary and comparison of methods for linewidth measurement

Table 3. Summary and comparison of methods for linewidth measurement

Table 2. $Δ f$ and $Δ S$ for different predicted linewidth and delaying fiber lengths^[31]

Table 2. $Δ f$ and $Δ S$ for different predicted linewidth and delaying fiber lengths^[31]