KR101312407B1 - Apparatus of generating laser light and method thereof - Google Patents

Abstract

PURPOSE: An apparatus and a method for generating a laser light source are provided to obtain real-time, high-speed, and high-resolution 3-dimensional images and to reduce the size and weight of the apparatus. CONSTITUTION: An apparatus for generating a laser light source comprises an optical fiber amplifier (135), a march-zender interferometer (MZI)(140), a wavelength selector (150), and an output coupler (160). The optical fiber amplifier amplifies and outputs incident light. The MZI generates optical beat frequencies from the light amplified by the optical fiber amplifier. The wavelength selector outputs multi-wavelength laser by converting or switching the wavelength of the outputted light of the MZI using optical fiber bragg grating. The output coupler sends the output of the wavelength selector to the optical fiber amplifier. The MZI contains a single mode optical fiber and two double cladding optical fibers. The double cladding fibers are arranged in both sides of the single mode optical fiber.

Description

Apparatus of generating laser light and method approx.

The present invention relates to an apparatus and method for generating a laser light source, and more particularly, to an apparatus and method capable of generating a mini optical comb with a close spacing between neighboring frequency peaks.

Optical coherence tomography (OCT), the next-generation precision imaging technology that can be applied to various industries such as medical diagnosis, industrial precision measurement, and non-destructive testing of agricultural and livestock products, has a resolution of several micrometers or less and existing medical images. It enables medical image acquisition of real-time high-resolution two-dimensional images of subcutaneous and vascular tissues, which are difficult to access with imaging techniques.

OCT technology is largely divided into Time-Domain OCT (TD-OCT) method and Frequency-Domain OCT (FD-OCT) method according to the principle of obtaining image information of living body. Recently, SS-OCT (Swept Source-OCT) technology using a wavelength sweeping laser light source, which is an FD-OCT method and has advantages of high quality and high speed image acquisition, has been in the spotlight.

To implement the SS-OCT wavelength sweeping laser light source, different wavelengths have to travel in the resonator of the laser over time. It is easy to control the tunable filter or rotating polygon scanner module to maintain the linearity of oscillation frequency versus time. not. For this reason, the existing SS-OCT system corrects the nonlinearity of the oscillation wave by performing a correction process on the obtained interference signal. Currently known correction methods are based on the fact that the frequency (or frequency k) interval is constant, although the time interval between two successive peaks of the interference signal varies. Based on this, a nonlinear graph of frequency (k _nonlin ) versus time (t) is obtained and correction is performed.

Other methods to compensate for nonlinear sweeping over time of oscillation frequency (or wavenumber) in SS-OCT systems include a semiconductor optical amplifier (SOA) in the 1310 nm band, Fiber Fabry Perot-Tunable Filter (FFP-TF), and fiber delay lines (FFP). Use a fiber delay line (FDML) for frequency swept ring lasers (e.g., fast reciprocating sweeping at 55.027 kHz, average output optical power at 9 mW, and wavelength sweeping at 125 nm). Configure.

OCT requires a wideband band laser light source that guarantees real-time, ultra-high speed, and high resolution functions, so a suitable light source determines the device's performance. For non-invasive cross-sectional imaging technology, a wavelength sweeping laser with wide bandwidth and fast sweeping speed has been required for SS-OCT systems, and the laser tuning range is 140nm at 10KHz sweeping speed and at 200KHz sweeping speed. A wavelength sweeping laser with an average power of 8mW at 100nm has been developed.

White LED Optical Frequency Combs, which are used in in vitro sample cross-sectional imaging techniques, are suitable for blood sampling and irradiation methods, but they are too powerful to penetrate flowing blood cells and are difficult to penetrate the skin. However, NIR LD Array can be used to analyze flow cytometry without collecting blood by simultaneously shining light, but this method has a disadvantage that it cannot scan a wide and deep area under the skin at high resolution.

As another light source, the continuous wave laser (CWL, Continuous) generated by changing the Zero Despersion Wavelength (ZDW) according to the length direction of the photonic crystal fiber There is a super continuous light (670 ~ 1350nm, 20W light pumping, 19.5W output) that is extended to the visible light region of the spectrum using a wavelength laser. However, it is important to inject sufficient optical power into the optical fiber because the principle of the generation of supercontinuous light is due to the capture of the dispersive wave related to the soliton magnetic frequency shifting effect. However, this requires high peak soliton pulse trains due to modulation instability, and even with a flat spectrum ranging from 650 to 1350 nm, this is too large for human applications. Supper Continum Laser light sources utilize Near Infrared (NIR) and can scan samples using MEMS (Micro Electro Mechanical Systems) mirrors and resonance vibrators, but their intensity is so strong that they can Not suitable for blood analysis.

Ultra-short femtosecond laser pulses are light generated based on the mode-locking principle, which has 10 ⁵ to 10 ⁶ resonant modes, and has a mode-locking property in which phases between modes match. In general, a Ti: Sapphire femtosecond laser with a 100nm bandwidth at 800nm center wavelength generates an ultrashort pulse of 9.42fs based on a Gaussian pulse. Mode locks of ultrashort femtosecond lasers with Ti: Sapphire photonic crystals as the gain medium are associated with nonlinear optical phenomena such as the Kerr effect which causes self focusing. In the time domain, saturable absorption, a nonlinear phenomenon similar to the Kerr effect, is associated, and in the frequency domain, self-phase modulation occurs in which the wavelength bandwidth is widened by the time-varying refractive index. .

Since nonlinear optical phenomena are proportional to the peak output and the optical fiber length in the optical fiber core, large mode area (LMA) optical fibers and photonic crystal optical fibers (PCF) have been used. Fiber-based ultrashort pulsed lasers are classified into three types: linear absorbers based on saturable absorbers, figure of eight resonators, and fiber ring resonators. The optical fiber ring resonator is a mode lock based on the nonlinear polarization rotation effect, in which the amount of rotation of the polarization changes according to the intensity of the pulse, and the pulse dispersion compensation circulation technique that forms a narrow pulse width and high output by controlling the dispersion of the pulse through the length of the optical fiber. Effectively perform ultrashort femtosecond pulses.

Fiber-based high power gain media have a great advantage in heat dissipation due to the large surface area-to-volume ratio, and the interaction between the seed laser and the pump laser extends to the length of the entire fiber without being limited to the Rayleigh length. Therefore, a high amplification rate can be obtained by a single pass. The use of optical fiber elements as pulse spreaders and compressors has the advantage of lower power amplification than using diffraction grating pairs. However, semiconductor optical amplifiers (SOA) or EDPA (Erbium-Doped Fiber Amplifiers) for the fabrication of ultra-short femtosecond laser pulse light sources are known as in vivo flow cytometry (FCM) during chirp-pulse amplification (CPA). ) Has the disadvantage of having a high output.

The elements widely used as gain media of near-infrared fiber lasers are Er (Erbium), Yb (Ytterbium), and Nd (Neodymium). The main oscillation wavelengths are 1550 nm of Erbium and 1060 nm of Yb. The ultra-short femtosecond laser pulses by the Fourier transform correspond to a wide wavelength bandwidth in the frequency domain, and the m-th frequency constituting the femtosecond laser optical comb since the pulse trains at regular intervals correspond to frequency modes arranged at equal intervals. mode (f _m) is by a mode between a repetition rate that corresponds to the distance (f _r, is detected by the photo detector) with the offset frequency corresponding to the difference from the absolute zero frequency (f _0, as measured by a non-linear f-2f interferometer) f _m It is simply defined as = mf _r + f ₀ . The optical fiber-based optical configuration is easy to align the light, greatly improves the stability of the optical comb operation, and can obtain a line width below mHz through dispersion optimization in the resonator and amplification stages, which is similar to the line width of the optical crystal optical comb. to be.

Domestic Publication No. 2012-0067618 Domestic Publication No. 2012-0044391

The technical problem to be achieved by the present invention is to generate a phase stabilized light source that can be used in a variety of fields, such as the medical field as well as micro-processing for in vivo analysis by providing a high resolution because the spacing between neighboring frequency peaks is dense A method and apparatus therefor.

In order to achieve the above technical problem, an example of a light source generating apparatus according to the present invention includes a laser light source generating apparatus comprising a loop type resonator, including: an optical fiber amplifier for amplifying and outputting incident light; A Mach-Zehnder interferometer for generating an optical bit frequency from light amplified by the optical fiber amplifier; A wavelength selection unit for converting or switching the wavelength of the output light of the Mach-Zehnder interferometer using an optical fiber grating to obtain a multi-wavelength laser output; And an output coupler for inputting a part of the output of the wavelength selector to the optical fiber amplifier.

In order to achieve the above technical problem, an example of a light source generation method according to the present invention, amplifying light using an optical fiber amplifier; Generating an optical bit frequency using an optical path difference due to reflection or transmission of the amplified light in a Mach-Zehnometer interferometer; Converting or switching the frequency of the light having the characteristic of the optical bit frequency into a comb-tooth pattern of equal spacing using an optical fiber grating; And injecting a portion of the frequency-converted or switched light back into the resonator.

According to the present invention, it is applied to the field of the OCT to enable the acquisition of real-time, high-speed, high resolution three-dimensional image, and provides miniaturization, light weight and cost competitiveness. In addition, it is possible to maintain the beam of diffraction limit, which is the most important feature of the fiber laser, and provides excellent heat emission effect and safe output to the human body.

1 is a view showing the configuration of an embodiment of a light source generating apparatus according to the present invention,
2 is a view showing the configuration of another embodiment of a light source generating apparatus according to the present invention;
3A and 3B are views showing an example of a detailed configuration of an optical fiber embedded Mach-Zehnder interferometer according to the present invention;
4 is a view showing an example of a detailed configuration of the wavelength selection unit according to the present invention, and
5 is a view showing an example of a laser light source generation method according to the present invention.

Hereinafter, a light source generating apparatus and a method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing the configuration of an embodiment of a light source generating apparatus according to the present invention.

Referring to FIG. 1, the light source generating apparatus includes a coupler 130 equipped with a noise rejection filter (NRF), an optical fiber amplifier 135, and a Mach-Zehnder interferometer 140 along a loop resonator 170. And a wavelength selector 150 and an output coupler 160. In addition, the configuration of supplying a laser to the resonator 170, the power supply device 100, current-optical converter 105, laser diode array (LDA) (110), sweeping laser (SSL, Swept Source Laser) 115 and an optical coupler 120.

First, the LDA 110 receives a current from the power supply 100 to generate a laser, and the SSL 115 receives light from the current-optical converter 105 that converts the current of the power supply 100 into light. Receives laser and generates laser. Here, as an example of the LDA, there is a broadband band superluminescent laser diode array (SLDA) having a center wavelength of 820 nm, 860 nm, and 1020 nm, and an example of SSL is Vernier-Tuned Distributed Bragg Reflector (VT-DBR). There is a wideband band swept laser having a structure of 1550 nm, 1310 nm or 1060 nm.

The optical coupler 120 combines the laser light of the LDA 110 and the laser light of the SSL 115 that are output through the optical fiber to the coupler 130 equipped with the NRF. As an example, the coupler couples the laser light of the LDA 110 and the laser light of the SSL 115 in a 2: 1.

Light whose signal-to-noise ratio (SNR) is improved through the NRF 130 is amplified by the optical fiber amplifier 135 and incident to the MZI 140. Here, an erbium doped optical fiber (EDF) or an erbium doped multi-wavelength optical fiber (MW-EDF) may be used as the optical fiber amplifier. Since EDF causes strong mode competetion and unstable oscillation due to its wide 'homogeneous gain broadening' at room temperature, it is very difficult to implement a multi-wavelength EDF laser. Therefore, EDF is required to reduce the 'homogeneous gain broadening' characteristic. Immersed in Liquid Nitrogen, Erbium Doped Twin-Core Fiber, Multiple Quantum-Well Waveguide, Elliptical Core EDF have.

The Mach-Zehnometer interferometer 140 combines the LLD and SSL 115 incident on the resonator when light of a predetermined wavelength, which has been passed through, reinforces the resonator 170 once and reaches the Mach-Zehnder interferometer 140 again. Optical bit frequencies are generated by synchronizing with each other to achieve the same wavelength as the light. The Mach-Zender Interferometer (MZI) will be described in detail with reference to FIG. 3.

The output beam of the Mach-Zehnder interferometer 140 is incident to the wavelength selector 150. The wavelength selector 150 converts the frequency using a fiber bragg grating (FBG) so that the frequency characteristics of the beam passing through the Mach-Zehnder interferometer 140 have a comb like shape with the same spacing. Switch. The wavelength selector 150 will be described in detail with reference to FIG. 4.

The output beam of the wavelength selector 150 is output to the output coupler 160. The output coupler 160 outputs a portion of the incident beam to the coupler 130 equipped with NRZ. For example, the output coupler 160 is a 90:10 coupler, and outputs 10% of the beam oscillated by the resonator 170 to the output terminal, and the rest of the coupler 130 equipped with the NRF through the 90% output terminal. Will output This causes the beam to oscillate in the ring resonator.

, 여기서,

는 에너지준위

에 있는 입자수)에 의하여

과 같이 나타난다. 증폭률(G)는 입사 레이저 강도가 약한 소 신호 증폭에서

(z는 증폭 매질의 길이)가 된다. Looking at the case in which the salping, the optical fiber amplifier 135 is composed of EDF in more detail, the amplification coefficient (g) of the EDF is the induced emission cross-sectional area (σ) and density inversion (

, here,

Energy level

By the number of particles in the

. Amplification factor (G) is for small signal amplification with weak incident laser intensity.

(z is the length of the amplification medium).

배의 이득을 얻는다.

는 빛이 매질 중에 단위거리를 진행할 때 증폭되는 비율이고 이득계수는

에 비례한다. 빛이 공진기내에서 왕복순환을 반복함으로써 강도의 증가를 이루고 있으므로 이득계수는 감소하고 최종적으로 빛의 강도는 일정한 값이 되고 따라서 레이저는 정상적인 발진상태에 도달한다. A laser oscillator or amplifier uses optical amplification by inductive emission. When light enters a medium having a density inversion, the light is amplified. The intensity of light increases exponentially with the propagation distance and the radiant light intensity in the medium of length L

Get a double benefit

Is the ratio amplified when light travels the unit distance in the medium, and the gain factor is

Proportional to Since the light increases in intensity by repeating the reciprocating cycle in the resonator, the gain coefficient decreases and finally the light intensity becomes a constant value, and thus the laser reaches a normal oscillation state.

2 is a diagram showing the configuration of another embodiment of a light source generating apparatus according to the present invention.

Referring to FIG. 2, the light source generating apparatus includes a wavelength division multiplexing unit (WDM) 210, an optical fiber amplifier 135, a Mach-Zehnder interferometer 140, and a wavelength selecting unit along a loop resonator 220. 150, an output coupler 160, and the like. The light source generator of FIG. 2 is different from FIG. 1 in the structure in which the laser light of the swept laser SSL or the laser diode LD is incident into the resonator through the wavelength division multiplexer 210 positioned in the resonator. Is the same as FIG. 1 and denoted by the same reference numerals.

An example of the wavelength division multiplexer 210 is a 980 nm / 1550 nm wavelength division multiplexer for an optical fiber coupler. The LD 220 outputting the laser to the resonator may be a laser diode with a laser center wavelength of 800 nm, 980 nm or 1480 nm, pumped with the current supplied from the power supply, and the SSL 220 pumped with light, the laser center It may be a broadband laser switching laser having a wavelength of 1550 nm, 1310 nm or 1060 nm.

3A and 3B are diagrams showing an example of a detailed configuration of an optical fiber embedded Mach-Zehnder interferometer according to the present invention.

Referring to FIGS. 3A and 3B, the Mach-Zehnometer interferometer (MZI) 300 includes a single mode fiber (SMF) 310 located between a double cladding fiber (DCF) 320 and 322. Structure (ie, DCF-SMF-DCF). The double cladding optical fibers 320 and 322 have two optical paths through the core 350 and the ring-shaped silica cladding mode. Strong cladding mode resonance through the inner cladding 352 is used to excite the cladding modes. The refractive index of the core 350 and the outer cladding 354 of the optical fiber is 1.4560, the diameters are 4.6 μm and 63 μm, respectively, and the refractive index of the inner cladding 352 is 1.4536 and the radius is 13.0 μm. The SMF-DCF lengths are 160mm and 48mm, respectively. When a fiber other than DCF is used in the resonator, long-period fiber gratings (LPFGs) 330 and 332 are positioned at both ends of the MZI.

The principle of generating the optical bit frequency in the Mach-Zehnder interferometer 140 is Frequency Domain Mode Locked (FDML) of the resonators 170 and 220. Looking more specifically through the equation, the free spectral range (FSR, Free Spectral Range) of the resonator (170,220) is as follows.

Where L _fiber is the total length of the resonators 170 and 220, n is the refractive index of the resonators 170 and 220, and c is the luminous flux at the vacuum speed.

는 다음 식과 같다.Change in the oscillation wavelength of light in the resonators 170 and 220

Is as follows.

은 중심 변조 진동수,

은 변조 진동수의 변화량이다.Where D is the variance variable,

Silver center modulation frequency,

Is the amount of change in the modulation frequency.

는 빛의 코히어런트 길이로서

이므로, 위 수학식 2의

를 이에 대입하면 다음과 같다.Theoretical value of optical axis resolution of SS-OCT

Is the coherent length of light

Since the above equation 2

Substituting this into:

)이 스위핑 속도(

)의 역수에 정수 배가 되어야 한다. 링 공진기(170,220)가 모두 광섬유로 구성되어 있다고 가정하면

이므로, 다음 수학과 같이 된다. In order to construct an FDML wavelength swept laser, the time required for the light emitted from the optical fiber amplifier 135 to rotate the resonators 170 and 220 in one rotation (

) Is the sweep speed (

Must be an integer multiple of reciprocal. Assume that the ring resonators 170 and 220 are all composed of optical fibers.

Therefore, it becomes as follows.

After being incident on the MZI, the light reflected or transmitted therein interferes with each other to generate an optical beat frequency due to an optical path difference in a wave number domain. A relationship as shown in Equation 5 below is established between the frequency interval Δf _comb (or FSR: Free Spectral Range) of the light passing through the MZI, that is, the transmission band, and the distance difference ΔL between the two reflected or transmitted light.

Where Δk is the frequency interval of the transmission band and c is the speed of light.

This is represented by Equation 6 again as a wavelength difference Δλ between transmission bands.

와 같이 주어진다.Is the wavelength of light, and the difference between the two optical paths in the air of MZI is

As shown in Fig.

In order to obtain an accurate cross-sectional image matching the actual structure from the optical bit frequency obtained in MZI, MZI provides a reference signal for correction. In general, when nonlinear sweeping of the laser oscillation frequency, the output signal of the MZI shows a chirped sinusoidal (comb) pattern whose frequency changes slightly with time.

의 속도로 Δλ_source 에 걸쳐 왕복 선형 스위핑을 수행한다면, MZI의 출력에서 얻어지는 빗살무늬 신호의 평균 주파수(

)는 다음 수학식과 같다.If SSL in the experiment

If we perform a reciprocal linear sweep across the Δλ _source at the rate of, then the average frequency of the comb

) Is as shown in the following equation.

When sweeping the wavelength of the swept light source, the chirped comb pattern output from the MZI is obtained, and the frequency difference between the comb peaks is the same over the entire comb pattern.

를 DCF(320,322)의

모드들의 합으로 표시하면, 다음과 같다.To understand the spread of light in the DCF (FIGS. 3, 320, 322), the basic mode of the SMF 310

Of the DCF (320,322)

Expressed as the sum of the modes,

은

의 전파상수이며,

은 SMF 모드

와 DCF 모드들

사이의 결합계수이다.here,

silver

Is the propagation constant of

SMF mode

And DCF modes

Coupling coefficient between

은 이중클래딩 광섬유를 따라 전파되며 그들의 다른 전파상수들 때문에 맥놀이를 일으킨다.Excited modes

Propagates along the double cladding fiber and causes beats due to their different propagation constants.

,

가 SMF

모드의 92% 에너지를 가짐이 알려져 있다. 그러므로 DCF의 투과스펙트럼은 이중모드 간섭과정으로 설명할 수 있으며, 이 이중모드 간섭은 코어와 외부 클래딩 모드 사이의 광파워 교환을 일으킨다. Most light energy is calculated by the first 10 modes, especially

,

SMF

It is known to have 92% energy of the mode. Therefore, the transmission spectrum of DCF can be explained by the bimodal interference process, which causes the optical power exchange between the core and the external cladding mode.

In general, since the SMF is longer than the DCF, the total phase difference in the optical fiber embedded MZI is mainly caused by the SMF, which is as follows.

,

는 각각 코어와 클래딩 모드들의 유효굴절률이다.here,

,

Is the effective refractive index of the core and cladding modes, respectively.

의 절반의 홀수 배이어야 한다. In order to maximize the contrast ratio of the interference spectrum, the coupling ratio of the two DCFs is required to be 3 dB, and according to the coupling mode theory, the DCF length is the beat length.

Should be an odd number of half of.

The FDML optical comb given by the above equation is incident to the wavelength selector 150 to obtain a stable multi-wavelength laser output.

4 is a view showing an example of a detailed configuration of the wavelength selection unit according to the present invention.

Referring to FIG. 4, the wavelength selector 150 includes an circulator 400, a polarization controller 410, and a chirped fiber bragg grating 420. And a pressure controller 430.

There is a method of connecting an inexpensive optical fiber grating (FBG) in an array by the wavelength selection element 150 of the resonators 170 and 220. As another example, multiple wavelengths can be obtained by changing the wavelength spacing by stretching or contracting the sample lattice, changing the wavelength spacing using a polarization maintaining optical fiber, and fabricating wavelength switching by fabricating FBG on a large birefringent optical fiber. There are methods for varying or switching the oscillation wavelength of an EDF laser, but these methods have disadvantages of using expensive or complicated laser structures.

4 shows a structure in which a multi-wavelength EDF ring laser can be stably oscillated by enabling wavelength conversion and switching while having a low loss, low nonlinearity, and easy reflection wavelength change. do.

Referring back to FIG. 4, the circulator 400 is vertically connected to the CFBG 420 having the polarization controller 410 in series, and the pressure controller 430 is a pressure applied to the CFBG 420. To control. The output beam of the Mach-Zehnder interferometer 140 enters the CFBG 420 through the circulator 400, and the beam reflected from the center wavelength of the CFBG 420 passes through the circulator 400 to output the coupler 160. Is output. At this time, by applying a pressure vertically to the CFBG 420 coupled in series with the polarization controller 410, the multiple wavelengths having the oscillation wavelength variability are simultaneously obtained.

More specifically, CFBG 420 is a variable optical element filter that selectively transmits or reflects a particular wavelength band in a wavelength division multiplexing system. Due to the birefringence caused by the pressure applied to the CFBG 420 perpendicular to the CFBG 420 by the pressure control unit 430, the optical fiber generates two different polarization states (that is, the direction in which the pressure is applied and Have The interval between the center wavelengths increases according to the strength of the pressure applied to the CFBG 420. The polarization characteristics in the optical fiber improve the inhomogeneous gain broadening characteristics of the EDF, so that the multi-wavelength EDF ring laser can perform stable multi-wavelength oscillation.

In addition, the polarization state of the beam incident on the CFBG 420 in the state where the pressure is applied to the CFBG 420 is adjusted through the polarization controller 410 to coincide with the direction in which the pressure is applied or the perpendicular direction thereof to each polarization state. The wavelengths that combine with can be switched independently. In other words, by changing the pressure applied to the CFBG 420 it is possible to continuously change the output wavelength and the wavelength interval, it is possible to switch the output wavelength to the appropriate wavelength by adjusting the polarization controller 410.

Looking at the principle that the birefringence occurs when the pressure is applied vertically to the CFBG 420 as follows.

2n pieces of oscillation wavelength conversion with narrow wavelength gap at room temperature using birefringence generated when n optical fiber gratings (FBG) are made on general optical fiber and pressure is applied to the optical fiber gratings vertically. The oscillation wavelength EDF ring laser can be configured.

When no pressure is applied to the optical fiber grating FBG, the reflection wavelength λ _B of the optical fiber grating FBG is as follows.

는 유효굴절률이고,

는 격자의 주기이다.here,

Is the effective refractive index,

Is the period of the grid.

On the other hand, when pressure is applied to the optical fiber, the effective refractive index of the optical fiber changes asymmetrically in the y-axis direction to which the pressure is applied and the x-axis direction perpendicular thereto due to the photoelastic effect, thereby causing birefringence. The amount of change in refractive index Δn _x and Δn _y in the _x- and y-axis directions is represented by the following equation.

는 압력이 인가되지 않았을 때의 초기 광섬유의 굴절률이며, E는 Young's modulus(

),

는 Poisson ration (0.17),

과

는 광탄성계수,

와

는 x축과 y축에 대한 각각의 응력광학계수(stress-optical coefficient)를 나타낸다.here,

Is the refractive index of the initial fiber when no pressure is applied, and E is Young's modulus (

),

Poisson ration (0.17),

and

Is the photoelastic coefficient,

Wow

Denotes the stress-optical coefficients for the x and y axes, respectively.

와 같으며, 인가되는 압력을 증가시킬수록 중심파장간의 간격도 커진다.When pressure is applied to the FBG, the center wavelength of the FBG is separated into two peaks corresponding to two axial directions due to the refractive index change as shown in the above equation. At this time, the interval of the separated center wavelength is

As the pressure increases, the distance between the center wavelengths increases.

커플러와 병렬로 연결하는 구조뿐만 아니라 1개의 PC를 직렬로 가진 1개의 CFBG를 커플러와 수직으로 연결한 구조에 압력을 가하여 파장변환과 스위칭을 구현할 수 있다.Therefore, n FBGs with 1 PC in series each

In addition to the structure connected in parallel with the coupler, wavelength conversion and switching can be realized by applying pressure to the structure in which one CFBG having a PC in series is connected vertically with the coupler.

At this time, the light source has a wide wavelength (780nm to 1650nm), each of the frequency peak line width in the frequency range is thin (level below mHz) and has bright energy (20mW) which is harmless to the human body, and the reflectance of each wavelength reflecting group of CFBG is 20%. It is preferable to comprise so that it may not exceed. For example, in this embodiment, the spacing between adjacent frequency peak that is very dense (10 ⁵ / 100nm), to generate a optical coherence tomography device for light pulses of the femtosecond (about 10fs hereinafter) in the time domain have.

5 is a view showing an example of a laser light source generation method according to the present invention.

Referring to FIG. 5, the laser light source generating apparatus configured as a loop resonator receives laser light such as SSL and LDA (S500). The resonator amplifies the incident laser light using the optical fiber amplifier (S510) and inputs it to the Mach-Zehnder interferometer (S520). The beam passing through the Mach-Zehnder interceptometer is generated by a multi-wavelength laser having a comb-tooth pattern of equal intervals through the CFBG (S530). Part of the generated multi-wavelength laser is incident again into the resonator and oscillates (S540).

The phase stabilized fiber laser light frequency comb (mini optical comb) produced by the present invention is used in the field of fine processing (for example, automotive, shipbuilding, aviation, heavy industry, electrical and electronics, semiconductor industry, etc.), optical communication field, and dentistry field. (Ultra wide band light source using OCT, Raman fiber laser, photonic crystal fiber, etc.). The invention is also applicable to equipment related to multiphoton microscopy (MPM), second harmonic generation wave (SHG) applications, Doppler optical coherence tomography (D-OCT), optical fluorescence periodic imaging microscope (FIIM), interference Inelastic Raman Scattering (CARS), Radiation Diagnostics, Optical Acoustic Microscope (PAM), Optical Thermography (PTM), LSCA, MRI, PET / CT, Wide-area Microscope, Confocal Microscope, Confocal or Multiphoton Endoscope Microscope, 4pi Microscope It can also be applied to SED0-M, stochastic optical reconstruction microscope, light activated local microscope.

Looking at the application of the medical field in more detail, it can be used as a light source for generating a mini optical comb for measuring blood cells in the blood vessels under the skin. In vivo Flow Cytometry (FCM) is involved in cell metabolism, immune function, and cellular apoptosis in biology, and in medicine, studies on cancer, bacterial infections, cardiovascular abnormalities, and purification of abnormal cells are carried out. To be added.

In vivo studies contrast with almost all ideal situations in in vitro studies. In vivo studies have poor optical conditions for absorption, scattering, and spontaneous fluorescence in perivascular tissues (skin layer, connective tissue, muscle, fat, etc.), the presence of multiple cell flows in the blood vessel cross-section, Difficulties in invasive approaches, problems of transmitting strong light in front or side to the tissue for high resolution, and safety in variables of blood or lymph flow. The solution of this problem has a very high correlation with the light source. Therefore, to measure blood cells in the blood vessels under the skin, the 'mini optical comb' generating device must meet the following requirements.

First, NIR light must be emitted at the same time, not in order of wavelength size. Second, when the wavelength is emitted instantaneously, the absorption wavelength is different depending on the material. Medium intensity absorption of the most suitable wet water spectrum should be used. Third, various types of OCT implementation methods use SS-OCT system to provide high speed image frame and high resolution.

A light source that meets these three requirements must have a broad wavelength (750nm to 1750nm) with a narrow (less than mHz) line width of each frequency peak in the frequency range and bright energy (less than 100mW) harmless to the human body. The pulses of the distance between adjacent peak frequencies which are very dense (10 ⁵ / 100nm), femtosecond (about 10fs hereinafter) in the time domain is needed. This is because a femtosecond laser uses a high power laser because it is harmful to cells and thus requires appropriate energy. Accordingly, the light source generating apparatus according to the present invention generates an FDML wavelength swept fiber laser having a high light output power, a wide wavelength sweeping range, and a narrow line width suitable for a human body. The laser thus generated is a phase stabilized Fourier region mode locked fiber laser light frequency light (FDML-FL-OFC), a so-called 'mini optical comb'.

So far I looked at the center of the preferred embodiment for the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: power supply 105: current-to-optical converter
110: laser diode array (LDA) 115: swept laser (SSL)
120: optical coupler 130: coupler with NRF
140: Mach-Zehnder interferometer 150: wavelength selector
160: output coupler 400: circulator
410: polarization controller (PC) 420: CFBG
430: strain controller

Claims (11)

delete In the laser light source generating device consisting of a loop type resonator,
An optical fiber amplifier for amplifying and outputting incident light;
A Mach-Zehnder interferometer for generating an optical bit frequency from light amplified by the optical fiber amplifier;
A wavelength selection unit for converting or switching the wavelength of the output light of the Mach-Zehnder interferometer using an optical fiber grating to obtain a multi-wavelength laser output; And
And an output coupler for inputting a part of the output of the wavelength selector to the optical fiber amplifier.
The Mach-Zehnder interferometer,
Single mode optical fiber; And two double-cladding optical fibers respectively positioned with the single-mode optical fiber interposed therebetween. In the laser light source generating device consisting of a loop type resonator,
An optical fiber amplifier for amplifying and outputting incident light;
A Mach-Zehnder interferometer for generating an optical bit frequency from light amplified by the optical fiber amplifier;
A wavelength selection unit for converting or switching the wavelength of the output light of the Mach-Zehnder interferometer using an optical fiber grating to obtain a multi-wavelength laser output; And
And an output coupler for inputting a part of the output of the wavelength selector to the optical fiber amplifier.
The wavelength selection unit,
A circulator for outputting light output from the Mach-Zehnder interferometer to a chirped fiber grating and outputting light reflected by the CFBG to the output coupler;
A pressure controller for applying a vertical pressure to the CFBG; And
And a polarization controller connected in series between the circulator and the CFGB. The method of claim 2 or 3, wherein the output coupler,
And a 90:10 coupler for injecting 90% of the output of the wavelength selector into the optical fiber amplifier and outputting the remaining 10% to the outside. According to claim 2 or 3, wherein the optical fiber amplifier,
An apparatus for generating a laser light source, characterized in that it is implemented with at least one of an erbium-doped optical fiber, an erbium-added dual core optical fiber, a multi-quantum source waveguide, and an elliptical core EDF. 4. The method according to claim 2 or 3,
Laser diode arrays and swept lasers having different center wavelengths; And
And a coupler for injecting the combined light of the laser diode and the swept laser into the optical fiber amplifier. The method according to claim 6,
And the output light of the laser diode and the output light of the swept laser are coupled through a 2: 1 optical coupler and incident to the coupler. 4. The method according to claim 2 or 3,
Laser diodes or sweeping lasers; And
And a wavelength division multiplexer for injecting the output light of the laser diode or the swept laser into the optical fiber amplifier. delete delete In the light source generating method of the light source generating device composed of a loop type resonator,
Amplifying the light using an optical fiber amplifier;
Generating an optical bit frequency using an optical path difference due to reflection or transmission of the amplified light in a Mach-Zehnometer interferometer;
Converting or switching the frequency of the light having the characteristic of the optical bit frequency into a comb-tooth pattern of equal spacing using an optical fiber grating; And
Injecting a portion of the frequency converted or switched light back into the resonator;
Synchronizing the light arriving at the Mach-Zehnder interferometer with one rotation of the resonator with a wavelength of light newly incident to the resonator;
Converting or switching the frequency,
Adjusting the spacing between the center wavelengths using the vertical pressure applied to the chirped fiber grating;
Adjusting a polarization state of light incident on the chirped optical fiber grating so as to coincide with two polarization states due to birefringence generated in the optical fiber by the vertical pressure; And
And independently switching wavelengths combined with each polarization state.

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