Reconfigurabletime-stretchedsweptlasersourcewithupto100MHzsweeprate,100nmbandwidth,and100mmOCTimagingrange资源-CSDN文库

187 浏览量 2021-02-21 22:48:31 上传评论收藏 4.4MB PDF 举报

资源推荐

资源详情

资源评论

Reconfigurable time-stretched swept laser source

with up to 100 MHz sweep rate, 100 nm

bandwidth, and 100 mm OCT imaging range

DONGMEI HUANG,

1,2

FENG LI,

1,2,

*CHAO SHANG,

2,3,4

ZIHAO CHENG,

1,2

AND P. K. A. WAI

1,2

Photonics Research Centre, Department of Electronic and Information Engineering, The Hong Kong Polytechnic University,

Hong Kong SAR, China

The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China

Photonics Research Centre, Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China

Key Laboratory of Luminescence and Optical Information, Ministry of Education, School of Science, Beijing Jiaotong University,

Beijing 100044, China

*Corresponding author: enlf@polyu.edu.hk

Received 7 February 2020; revised 31 May 2020; accepted 17 June 2020; posted 18 June 2020 (Doc. ID 390076); published 23 July 2020

The sweep rate, sweep range, and coherence length of swept sources, respectively, determine the acquisition rate,

axial resolution, and imaging range of optical coherence tomography (OCT). In this paper, we demonstr ate a

reconfigurable high-speed and broadband swept laser by time stretching of a flat spectrum femtosecond pulse

train with over 100 nm bandwidth and a repetition rate of 100 MHz. By incorporating an optical modulator and

utilizing appropriate dispersive modules, the reconfiguration of the swept source is demonstrated with sweep rates

of 25 and 2.5 MHz. The 2.5 MHz swept source enables an imaging range of >110 mm with 6 dB sensitivity roll-

off in OCT, which is the longest imaging range ever reported for megahertz OCT.

https://doi.org/10.1364/PRJ.390076

1. INTRODUCTION

Swept source optical coherence tomography (SS-OCT) is the

most promising technology for next-generation OCT since it

does not rely on any moving reference mirror, and has higher

spectral resolution and acquisition rate than spectrometer-based

spectral domain OCT [1,2]. SS-OCT adopts a high-speed bal-

anced detector to acquire time-resolved interference signal and

obtain the layered image of the sample with the Fourier trans-

form of the interference spectrum. The key component of the

SS-OCT system is the swept laser with a high sweep rate, wide

sweep range, and long coherence length.

A variety of wavelength swept lasers have been developed for

megahertz SS-OCT systems [1]. Conventional tunable lasers

have a limited sweep rate owing to the limitation of the buildup

of the new laser signals during the wavelength tuning. When a

micro-electro-mechanical system (MEMS) structure is com-

bined with the vertical cavity surface emitting laser (VCSEL),

the sweep rate could be enhanced to >500 kHz [3,4] to enable

a megahertz axial scan (A-scan) rate of SS-OCT. The VCSEL

swept source also demonstrates a long coherence length to ex-

tend the imaging range of OCT to a few meters [5]. However,

the sweep rate of VCSEL is hard to enhance to >1 MHz with

practical sweep range because of the inertia limitation [3,4].

The high driving voltage, the nonlinear tuning response,

and the low output power are the problems in the development

of wavelength swept VCSELs. In 2006, Fourier domain mode-

locked (FDML) laser was proposed to avoid the rebuilding of

intracavity laser signals and enhance the fundamental sweep

rate to ∼300 kHz [6]. The sweep rate of the FDML laser-based

swept source could be enhanced to 6.7 MHz with a high-order

buffering technique, but the sweep range is reduced to <50 nm

[7]. The major weakness of the FDML laser is the short coher-

ence length [8,9]. Although state-of-art dynamic compensation

of the cavity dispersio n could significantly enhance the coher-

ence length, it is very challenging to maintain the stable swept

signal [10,11]. Discretization of the swept signal by comb filters

[12] could extend the coherence length to >100 mm [13].

However, the resolving of absolute positions of the images is

the major challenge in the application of such swept sources [14].

To further enhance the sweep rate, time stretching of broad-

band ultrashort pulses is a more promising technique [15].

In 2006, Moon and Kim proposed to stretch a wideba nd super-

continuum pulse source in the time domain by a long disper-

sive fiber based on group velocity dispersion, of which the

sweep rate could reach 5 MHz [16]. Time stretching of pulses

generated by a mode-locked fiber laser could generate swept

signals with ultrahigh sweep rate [17,18]. However, it is still

challenging to obtain a highly coherent pulse source with a suf-

ficiently wide spectrum because of the gain bandwidth limita-

tion of the rare-earth doped fibers and strong nonlinear noise.

1360

Vol. 8, No. 8 / August 2020 / Photonics Research

Research Article

Many efforts have been paid to extend the sweep range by de-

veloping a broadband mode-locked fiber laser and combining

other nonlinear spectral expansion [17–20]. In 2018, Kang

et al. reported a 44.5 MHz time-stretched swept source with

a 10 dB bandwidth of 102 nm, which had the highest sweep

rate ever reported for time-stretched swept sources with a prac-

tical sweep range of ∼100 nm [21]. But, the spectrum gener-

ated from the mode locked fiber laser has a large slope, and the

3 dB bandwidth is only ∼30 nm.

In this paper, we will demonstrate a reconfigurable time-

stretched swept source based on a 100 MHz Figure-9 mode

locked fiber laser with 100 nm sweep range. In Section 2,

we will introduce the experimental setup of the reconfigurable

swept source and the point spread function (PSF) characteri-

zation. Three configurations of the swept source with sweep

rates of 2.5–100 MHz will be demonstrated in Section 3.

The sensitivity roll-off of the OCT based on the swept sources

will be characterized by the PSFs. Conclusions will be drawn in

Section 4.

2. EXPERIMENTAL SETUP

A. Reconfigurable Time-Stretched Swept Source

Figure 1 shows the experimental setup of the swept laser, where

a femtosecond mode-locked laser with a consecutive fiber am-

plifier is used as the seed signal of the system. An optical modu-

lator combined with a pulse/pattern generator (PPG, Agilent,

81130A) is used to realize frequency division. A dispersion

compensation module, which is either a section of dispersion

compensation fiber (DCF) or a long chirped fiber Bragg grating

(CFBG), is used to realize time stretching. The mode-locked

laser is a custom-built Figure-9 laser (Menlo System, C-Fiber)

with a dispersion matched erbium-doped fiber amplifier

(EDFA), where the dispersions of the seed laser and fiber am-

plifier are carefully engineered to guarantee that the output

pulse has a broad spectrum with 3 dB bandwidth of ∼80 nm.

Compared with the conventional femtosecond mode-locked

fiber lasers based on the nonlinear amplified loop mirror (NALM)

or nonlinear polarization rotation (NPR), the Figure-9 laser is

much more stable since an all polariz ation maintaining fiber

cavity is adopted [22]. Another advantage of such a configura-

tion is the low loss working point on the transmission curve,

which lowers the threshold to start mode locking [22]. The

maximum transmission is achieved by the combination of a

45° Faraday rotator, a wave plate, a polarizing beam splitter,

and a mirror. When a wave plate with a single pass phase re-

tardation of π∕4 is used, the small signal in the laser cavity

works with the largest slope on the nonlinear transmission

curve. With such a highly efficient cavity, a chirped pulse with

a bandwidth of >40 nm is generated from the seed laser. The

100 MHz repetition rate obtained with the compact cavity is

much higher than that of conventional lasers with NPR or

NALM configurations. The chirped pulse is then injected into

the EDFA to simultaneously amplify and compress the pulse to

<50 fs, where the spectrum is further broadened to have a 3 dB

bandwidth of 77 nm at the output.

The reconfiguration of the sweep rate is realized by

modulating the 100 MHz optical pulse train with a low

repetition rate electric pulse train. A 10 GHz LiNbO

Mach–Zehnder optical intensity modulator (JDS Uniphase,

IOAP-MOD9140) is used after the EDFA to modulate the op-

tical signal. A variable optical attenuator (ANDO, AQ-3105A)

is utilized before the modulator to decrease the optical power in

order to avoid nonlinear effects, which could deteriorate the

coherence and simultaneously induce fluctuations on the spec-

trum. A small part of the output signal from the mode-locked

fiber laser is injected into a photodetector to generate a clock

signal with frequency f  100 MHz for the PPG, which is

used to generate a sequence of short square pulses with frac-

tional frequency f ∕N, where N  1, 2, 3, … is an integer.

By adjusting the number of ‘0’ bits (off) between adjacent

‘1’ bits (on) in the pattern, the repetition rate of the electric

pulse train can be reconfigured. An optical modulator driver

(JDS Uniphase, H301-1110) is used to amplify the electric

pulse train to drive the modulator and an automatic bias con-

troller (Plugtech, MBC-IQ-1) is used to dynamically lock the

bias voltage at the “NULL” point of the modulator to ensure

that the optical pulses at the “off ” bits are completely su p-

pressed. The polarization dependence of the modulation is con-

trolled by a polarization controller.

The time stretching is the key process, where the ultrashort

pulses are stretched by the dispersion modules such as a section

of DCF or a CFBG to highly chirped long pulses with a sweep

trace of [16]

tλt

 L

Dλ

dλ

, (1)

where D is the group velocity dispersion coefficient and L is the

fiber length (only nominal for CFBG). The duration of the

output pulse is

Frequency dividing

Pump

PBS

Components

Mirror

EDF

WDM

OSA

OSC

CFBG

DCF

20km

200km

VOA

MOD

PPG Bias

EDFA

Driver

Sync.

Mode locked laser

Time Stretching

Fig. 1. Experimental setup of the swept laser. WDM, wavelength di-

vision multiplexer; EDF, erbium-doped fiber; PBS, polarizing beam

splitter; Components, Faraday rotator, wave plate, and polarizing beam

splitter; OC, optical coupler; EDFA, erbium-doped fiber amplifier;

VOA, variable optical attenuator; PC, polarization controller; PPG,

pulse/pattern generator; MOD, optical modulator; CFBG, chirped fiber

Bragg grating; DCF, dispersion compensation fiber; PD, photodetector;

OSA, optical spectrum analyzer; OSC, oscilloscope.

Research Article

Vol. 8, No. 8 / August 2020 / Photonics Research 1361

剩余7页未读，继续阅读

评论收藏

内容反馈

weixin_38624628

粉丝: 8
资源: 934

Reconfigurable time-stretched swept laser source with up to 100 ...

最新资源

Reconfigurable time-stretched swept laser source with up to 100 ...

sweep frequence

Frequency-locked tunable LD laser with a broad bandwidth

Tunable bandwidth optical rotator

A Mapping Flow for Dynamically Reconfigurable Multi-Core System-on-Chip

A Reconfigurable Beam-Scanning Partially Reflective Surface (PRS) Antenna

System Level Design of Reconfigurable Systems-on-Chip

（可重构）RECONFIGURABLE Computing--THE THEORY AND PRACTICE OFFPGA-BASEDCOMPUTATION

towards-artificial-general-intelligence-with-hybrid-tianjic-chip-architecture

Modeling of Gaussian Network-Based Reconfigurable Network-on-Chip Designs

Cognitive-Radio-Experiments-using-Reconfigurable-_Reconfigurable

基于阿基米德螺旋推进的ARCNAKE可重构蛇形机器人多域移动_ARCSnake Reconfigurable Snake-Lik

Improving Nested Loop Pipelining on Coarse-Grained Reconfigurable Architectures

Reconfigurable nano-kirigami metasurfaces by pneumatic pressure

90 branch-kine coupler with reconfigurable output power rations

PSoC® 6 MCU: PSoC 63 with BLE Datasheet

ISSCC2017-02

A Reconfigurable FM-UWB Transceiver for Short-Range Wireless Communications

An On-Line Reconfigurable Four-Ary Tree-Based Network on Chip for Distributed Particle Filters

Elphel reconfigurable cameras-开源

All-optical reconfigurable multi-logic gates based on nonlinear polarization rotation effect in a single SOA

Robotic Building (Springer Series in Adaptive Environments)

Guiding and routing of a weak signal via a reconfigurable gravity-like potential

Advanced Mechatronics and MEMS Devices II 2017.pdf

Photonic-assisted wideband frequency downconverter with self-interference cancellation and image rejection

Reconfigurable continuous-zoom metalens in visible band

Reconfigurable non-blocking four-port optical router based on microring resonators.

A Bandwidth Broadened Pattern-Reconfigurable Antenna Based on Graphene

最新资源