Broadband all-fiber optical phase modulator based on photo-thermal effect in a gas-filled hollow-core fiber

Shoulin Jiang; Feifan Chen; Yan Zhao; Shoufei Gao; Yingying Wang; Hoi Lut Ho; Wei Jin

doi:10.29026/oea.2023.220085

Journals >Opto-Electronic Advances >Volume 6 >Issue 5 >Page 220085 > Article

Opto-Electronic Advances
Vol. 6, Issue 5, 220085 (2023)

Broadband all-fiber optical phase modulator based on photo-thermal effect in a gas-filled hollow-core fiber

Shoulin Jiang¹, Feifan Chen^1,2, Yan Zhao^1,2, Shoufei Gao³..., Yingying Wang³, Hoi Lut Ho^1,2 and Wei Jin^1,2,*|Show fewer author(s)

Author Affiliations

¹Photonics Research Center, the Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China

²Department of Electrical Engineering and Photonics Research Institute, the Hong Kong Polytechnic University, Hong Kong 999077, China

³Institute of Photonics Technology, Jinan University, Guangzhou 510632, China

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DOI: 10.29026/oea.2023.220085 Cite this Article

Shoulin Jiang, Feifan Chen, Yan Zhao, Shoufei Gao, Yingying Wang, Hoi Lut Ho, Wei Jin. Broadband all-fiber optical phase modulator based on photo-thermal effect in a gas-filled hollow-core fiber[J]. Opto-Electronic Advances, 2023, 6(5): 220085 Copy Citation Text

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(a) Schematic showing the principle of HCF-based PT phase modulator. (b) Calculated absorption coefficient of the P(9) line of pure C2H2 at 1 atm as a function of T by use of HITRAN database22. (c) Transverse distribution of T and p calculated by using COMSOL Multiphysics with Pctrl=500 mW and f=100 kHz. (d) Variation of local phase modulation with a step length of 1 mm and accumulated phase modulation along the length of an acetylene-filled HCF.

Fig. 1. (a) Schematic showing the principle of HCF-based PT phase modulator. (b) Calculated absorption coefficient of the P(9) line of pure C₂H₂ at 1 atm as a function of T by use of HITRAN database²². (c) Transverse distribution of T and p calculated by using COMSOL Multiphysics with P_ctrl=500 mW and f=100 kHz. (d) Variation of local phase modulation with a step length of 1 mm and accumulated phase modulation along the length of an acetylene-filled HCF.

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(a) Schematic diagram and (b) photo of the fabricated gas-filled hollow-core fiber phase modulator. (c) Measured loss spectrum of the phase modulator. (d) Experimental setup for characterizing the phase modulator. TECF: thermal-expanded core fiber, DFB: distributed feedback laser, FG: function generator, AOM: acoustic optical modulator, EDFA: erbium-doped fiber amplifier, WDM: wavelength-division multiplexer, PZT: piezoelectric transducer, PC: polarization controller, PD: photodetector, OSC: oscilloscope, LPF: low-pass filter.

Fig. 2. (a) Schematic diagram and (b) photo of the fabricated gas-filled hollow-core fiber phase modulator. (c) Measured loss spectrum of the phase modulator. (d) Experimental setup for characterizing the phase modulator. TECF: thermal-expanded core fiber, DFB: distributed feedback laser, FG: function generator, AOM: acoustic optical modulator, EDFA: erbium-doped fiber amplifier, WDM: wavelength-division multiplexer, PZT: piezoelectric transducer, PC: polarization controller, PD: photodetector, OSC: oscilloscope, LPF: low-pass filter.

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Fig. 3. Characteristics of the HCF-based PT phase modulator with a modulation frequency of 100 kHz. (a) MZI output waveforms with different P_ctrl in the AR-HCF. (b) Phase modulation amplitude as a function of P_ctrl. (c) Wavelength dependence of phase modulation amplitude for P_ctrl=502 mW.

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Fig. 4. (a) Frequency response of phase modulation with P_ctrl =502 mW. (b) Transient response detected by use of the MZI for control light beam pulse width of 50 μs.

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Material	Acetylene		Silica		Air
TemperatureT [K]	300	400	300	400	300	400
Density ρ [kg/m³]	1.04	0.78	2203	2203	1.16	0.85
Thermal conductivityκ [W/(m·K)]	0.0214	0.0333	1.38	1.48	0.0262	0.0333
Heat capacity C_p [J/(kg·K)]	1699	1938	746	891	1007	1018

Table 0. Temperature-dependent thermodynamic parameters of materials at 1 atm^25,26.

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Ref.	Physical effect	Fiber type	Functional material	Phase change (rad)	Rise/fall time constant	Insertion loss
^apeak phase modulation for a step change of control power, ^bdynamic phase modulation measured at 100 kHz.
ref.⁵	Kerr	MF	Graphene	0.18π@1.15 W^a	a few ns	10 dB@1550 nm
ref.⁸	PT	MF	Graphene	21π@230 mW^a	4.0/1.4 ms	5.4 dB@1540 nm
ref.⁹	PT	MF	Phosphorene	8π@290 mW^a	2.5/2.1 ms	10 dB @1550 nm
ref.¹⁰	PT	MF	WS₂	6π@345 mW^a	7.3/3.5 ms	3.5 dB@1550 nm
ref.¹¹	PT	MF	Bismuthene	22π@420 mW^a	3.4/3.4 ms	5.5 dB@1550 nm
ref.¹²	PT	MF	Boron nanosheet	4π@300 mW^a	0.48/0.69 ms	5.5 dB@1550 nm
ref.¹³	PT	MF	BQDs	10π@315 mW^a	0.5/0.6 ms	Not given
This work	PT	AR-HCF	C₂H₂	π@289 mW^b	3.5/3.7 μs	0.6 dB@1550 nm