JP6831773B2 - Wavelength sweep light source - Google Patents

Description

The present invention relates to a wavelength sweeping light source in which a momentarily narrow spectrum is periodically swept on the wavelength axis.

A swept source OCT (SS-OCT) using a wavelength sweeping light source in which a narrow laser spectrum is periodically swept on the wavelength axis is used as a method of optical coherence tomography (OCT). is there. SS-OCT is known as a form of Fourier domain OCT (FD-OCT) that does not require a spectroscope.

In the spectral domain OCT (SD-OCT), which is another form of FD-OCT, the interference signal is separated and the OCT signal is obtained as a spatial light intensity distribution. In this case, a high-resolution array detector is used for light detection. You will need it. The OCT signal here is a signal including fault information, and the spatial frequency of the intensity distribution changes according to the delay difference between the two light waves at the time of interference.

On the other hand, in SS-OCT, since the spectrum of the narrow line width light source is swept directly on the wavelength or frequency axis in time, it can be regarded as being separated in time, and the time waveform is obtained by a general photodetector. The OCT signal can be acquired as. The depth information corresponds to the frequency of the interference signal as it is. Therefore, it is mainly used in OCT having a wavelength longer than near infrared, such as 1 μm band or 1.3 μm band, in which the imaging speed of SD-OCT is limited by the speed of the array detector.

What is important in SS-OCT using a wavelength sweep light source is the instantaneous laser line width of the wavelength sweep light source related to the measurement limit depth in the depth direction. The reciprocal of this instantaneous line width is proportional to the coherence length, and when the depth of the reflection point inside the observation target corresponds to 1/4 of the coherence length, the OCT signal is attenuated by 6 dB, so it is used as an index showing the dynamic range in the depth direction. Used.

In general, it takes a certain amount of time for the laser to oscillate and the line width to narrow, so in a wavelength sweep light source where the oscillation wavelength constantly changes, the laser line width may have a trade-off relationship with the sweep speed. It has been reported (see Non-Patent Document 1). That is, in a wavelength sweep light source having a high sweep frequency, the wavelength changes rapidly with time, the orbit time allowed for each wavelength is short, and the number of orbits is also reduced, so that the laser line width is widened.

A technique for breaking this trade-off relationship is a Fourier domain mode lock (FDML) laser (see Non-Patent Document 2). The FDML laser employs a light source system that extracts a part of the amplified light from the cavity, and its basic components are an optical amplifier, a wavelength selector, an optical delayer, and a part of the optical power from the cavity. Includes a light take-out device. These components are optically connected by light propagation such as free space or waveguide. The wavelength selector determines the instantaneous wavelength and the change in wavelength, and the wavelength sweep is realized by continuously changing the wavelength.

In the optical delayer, the light is delayed by a time corresponding to one sweep cycle of the wavelength selector or an integral multiple thereof. As a result, the sweep operation of the wavelength selector and the optical circuit can be synchronized, and the laser light of all wavelengths in the sweep band can be stored in the resonator. Therefore, even when the sweep frequency is high, the laser line width can be narrowed by the cumulative filtering effect in the wavelength selector without reducing the number of times around the optical resonator.

Japanese Patent No. 4751389

R. Huber, M. Wojtkowski, K. Taira, JG Fujimoto, and K. Hsu, “Amplified, frequency swept lasers for frequency domain reflectometry and OCT imaging: design and scaling principles,” Opt. Express 13, 3513-3528 (2005) ) R. Huber, M. Wojtkowski, and J. G. Fujimoto, “Fourier Domain Mode Locking (FDML): A new laser operating regime and applications for optical coherence tomography,” Opt. Express 14, 3225-3237 (2006)

The operating condition of this FDML laser is that the sweep frequency of the wavelength selector matches the free spectral range (FSR) determined by the optical cavity orbit time or an integral multiple of the FSR. Since the sweep frequency of a general wavelength sweep light source for OCT is several tens to several hundreds kHz, the optical delayer needs to have an optical path length of several km in order to obtain an FSR corresponding to this. An optical fiber is suitable when giving an optical delay of this length.

However, when a long optical fiber is used, the resonator length is likely to change, which causes a problem that a synchronization shift between the circumferential period of the ring resonator and the sweep period of the wavelength filter occurs. In an optical fiber having a length on the order of km, even a minute temperature change causes a non-negligible synchronization shift for FDML operation. Therefore, in order to realize stable operation and a narrow laser line width in the conventional FDML laser, it is necessary to control the temperature of the entire resonator including the long optical fiber.

Generally, temperature control requires a large output in proportion to the volume of the controlled object, but since the FDML laser needs to be stabilized in a very narrow temperature fluctuation range, a large-scale temperature control device is also required. Therefore, the conventional FDML laser has a problem in stable operation and cost reduction.

The present invention has been made in view of such a problem, and an object of the present invention is a wavelength sweep light source that realizes stable FDML operation by controlling the optical path length of the resonator according to a change in the resonator length. Is to provide.

In order to solve the above problems, the wavelength-swept light source according to an aspect of the present invention, an optical amplifying section for emitting light of Jo Tokoro wavelength band, among the light emitted from the optical amplification unit, a predetermined A wavelength selection unit that changes the selected wavelength according to the wavelength sweep frequency and the light output from the wavelength selection unit are branched into two, one branched light is returned to the optical amplification unit, and the other branched light is used as output light. The first optical branching unit to be output, the optical delay unit arranged between the optical amplification unit and the wavelength selection unit, and the optical path length adjustment arranged between the optical amplification unit and the wavelength selection unit. A stabilizing mechanism unit that controls the wavelength selection unit so as to adjust the optical path length of the resonator unit including the unit and the optical path length adjusting unit at least according to a change in the optical path length of the optical delay unit. light source unit and the optical delay unit light and the reference light multiplexes inputted to after wavelength selection by the wavelength selection unit that outputs a reference light intensity-modulated by the swept frequency, the wavelength selection Light detection that measures the light intensity of the reference light demultiplexed by the optical demultiplexing unit and the optical demultiplexing unit that demultiplexes the reference light output from the optical delay unit before selecting the wavelength in the unit. The phase difference between the light intensity signal wavelength of the reference light output from the light detection unit and the intensity modulation signal waveform of the light source unit is set to the phase difference when the output light reaches the maximum or a predetermined value. so as to be characterized by including a stabilizing mechanism including a feedback control unit for adjusting an optical path length of the optical path length adjusting unit. In this wavelength sweeping light source, the optical demultiplexing unit includes a dichroic mirror that reflects light having a wavelength of the reference light and does not reflect light having a wavelength of light emitted from the optical amplification unit, and the stabilizing mechanism unit includes a dichroic mirror. The reference light immediately after being output from the light source unit is linearly polarized light, and the polarized beam splitter includes the reference light immediately after being output from the light source unit. Is arranged so as to reflect light having a polarization axis rotated by 90 degrees with respect to the polarization axis of the reference light immediately after being output from the light source unit, and the reference light output from the light source unit is After passing through the polarized beam splitter, the light is converted into circularly polarized light through the 1/4 wavelength plate, then combined at the optical demultiplexing section, and demultiplexed at the optical demultiplexing section. Is linearly polarized to be a polarization axis rotated 90 degrees with respect to the polarization axis of the reference light immediately after being output from the light source unit on the 1/4 wavelength plate, and then reflected by the polarization beam splitter. It is preferable that the light is incident on the light detection unit. Alternatively, in this wavelength sweep light source, the optical demultiplexing unit includes a dichroic mirror that reflects light having a wavelength of the reference light and does not reflect light having a wavelength of light emitted from the optical amplification unit, and the stabilizing mechanism. The unit includes an isolator and a beam sampler, and the reference light output from the light source unit is transmitted in the order of the isolator and the beam sampler, and then combined at the optical demultiplexing unit, and the optical demultiplexing unit is used. The reference light demultiplexed in the section is partially reflected by the beam sampler and incident on the light detection section, and the reference light transmitted through the beam sampler is incident on the light source section by the isolator. It is preferable to prevent this from happening.

In another aspect according to any one of the above of the present invention, the feedback control unit performs the optical path when the light intensity signal waveform of the reference light is time-lagging with respect to the intensity modulated signal waveform of the light source unit. The optical path length of the optical path length adjusting unit is shortened, and the optical path length of the optical path length adjusting unit is lengthened when the light intensity signal waveform of the reference light is temporally advanced with respect to the intensity modulated signal waveform of the light source unit. It is a feature.

In another aspect according to any one of the above of the present invention, the reference light has a frequency that does not fall within the amplification band of the optical amplification unit.
It is characterized by lengthening the optical path length of the length adjustment unit.

In another aspect according to any one of the above of the present invention, the wavelength selection unit includes a KTN light deflector and a diffraction grating.

According to the present invention, by controlling the optical path length of the resonator according to the change in the resonator length as a synchronization method of the FDML laser, stable FDML operation can be realized without using a temperature controller.

It is a figure which shows the structural example of the wavelength sweep light source which concerns on Embodiment 1 of this invention. It is a figure which shows the structural example of the wavelength sweep light source of another aspect which concerns on Embodiment 1 of this invention. (A) is a diagram showing the phase change between the intensity signal of the reference light orbiting the fiber ring and the drive signal of the KTN optical deflector, and (B) shows the relationship between the phase difference Δφ and the optical path length of the fiber ring. It is a figure. It is a figure which shows the structural example of the wavelength sweep light source which concerns on Embodiment 2 of this invention.

Hereinafter, embodiments of the present invention will be described in detail.

(Embodiment 1)
FIG. 1 shows a configuration example of a wavelength sweep light source according to the first embodiment of the present invention. The wavelength sweep light source of the first embodiment is an FDML laser using a ring resonator. The FDML laser unit is composed of an isolator 110, an optical amplifier 120, a wavelength filter 130, an optical coupler 160, an optical delay fiber 170, a fiber ring constituting a ring resonator in which a fiber stretcher 180 is arranged, and light included in the wavelength filter 130. A driver device 140 for driving the deflector 133 is provided. Further, the ring fiber including the optical delay fiber 170 is configured to hold the polarized state of the circulating light by using the polarization holding fiber (PM fiber). In the first embodiment, in addition to the FDML laser unit, the fiber stretcher 180 is further controlled so that the difference between the circumferential period of the fiber ring and the sweep period of the wavelength filter 130 is an integral multiple of 1 or more becomes a predetermined value. A stabilization mechanism 150 for adjusting the optical path length of the fiber ring is provided.

The stabilization mechanism 150 of the first embodiment includes a laser light source 151 that outputs reference light, an intensity modulator 152 that modulates the intensity of reference light, and a polarizing beam splitter 153 that reflects only reference light that orbits a fiber ring, 1/4. Wave plate 154, dichroic mirror 155, photodetector 156 that detects the intensity of the reference light that orbits the fiber ring, delay line 157, phase change between the intensity signal of the reference light that orbits the fiber ring and the drive signal of the KTN optical deflector 133. A phase difference meter 158 and a feedback controller 159 are provided. The wavelength of the light output from the laser light source 151 is set so as not to fall within the amplification band of the optical amplifier 120 so that the dichroic mirror 155 can reflect only the light output from the laser light source 151.

The reference light output from the laser light source 151 is linearly polarized light having a predetermined polarization axis, and the intensity is synchronized with the sweep cycle of the wavelength filter 130 by the drive signal output from the driver device 140 in the intensity modulator 152. It is modulated. Further, the polarization beam splitter 153 transmits the reference light output from the intensity modulator 152 and directs light having a polarization axis rotated 90 degrees with respect to the polarization axis of the reference light output from the intensity modulator 152 in a predetermined direction. Arrange so that it reflects to.

In the FDML laser unit, naturally emitted light having a wide spectrum is output from an optical amplifier 120 having an optical amplification effect in a wavelength region equal to or larger than the sweep bandwidth of the wavelength sweep light source, and a circulator 131 is used to connect the wavelength filter 130 which is a free space optical system to the wavelength filter 130. be introduced.

The light introduced into the wavelength filter 130 is made into parallel rays by the collimator lens 132 arranged at the exit end of the fiber, and then incident on the potassium niobate (KTN) light deflector 133 and the diffraction grating 134. The light reflected by the diffraction grating 134 is returned to the fiber ring via the circulator 131, and a part of the light is taken out from the fiber ring by the optical branching element 160, which becomes the output light of the wavelength selection light source. The remaining light follows the fiber ring again, passes through the optical delay fiber 170, and is returned to the optical amplifier 120 via the isolator 110. At this time, the ring fiber including the optical delay fiber 170 is a polarization-holding fiber (PM fiber), and the light circulating around the fiber ring maintains a polarization state that matches the polarization dependence of the KTN optical deflector 133.

The wavelength filter 130 performs a wavelength selection operation according to a drive voltage waveform (for example, a sine wave having a frequency of 200 kHz) from the driver device 140. That is, the wavelength filter 130 is swept periodically, and the length of the optical delay fiber 180 is the same as or an integral multiple of the sweep period of the wavelength filter 130 in the time required for light to go around the entire resonator. As a result, the light having the wavelength selected by the wavelength filter 130 goes around the fiber ring and then passes through the wavelength filter 130 again, which coincides with the timing of selecting the same wavelength for the next sweep of the wavelength filter 130, and again with the minimum loss. You can receive the filtering effect. This phenomenon occurs at all wavelengths within the sweep band.

In the stabilization mechanism 150, the reference light output from the laser light source 151 passes through the polarization beam splitter 153, is converted into circularly polarized light by the 1/4 wave plate 154, is reflected by the dichroic mirror 155, and is reflected from the fiber collimator 132 to the fiber. Input to the ring. The reference light that orbits the fiber ring is reflected by the dichroic mirror 155, converted into linearly polarized light that is rotated 90 degrees with respect to the polarization axis of the reference light output from the intensity modulator 152 by the 1/4 wavelength plate 154, and is polarized. It is reflected by the beam splitter 153 and incident on the photodetector 156. The light intensity signal output from the photodetector 156 is input to the phase difference meter 158 together with the drive signal output from the driver device 140.

At this time, the drive signal output from the driver device 140 is input to the phase difference meter 158 via the delay line 157 for compensating for the deviation of the arrival time to the phase difference meter 158 due to the difference in the circuit configuration. The feedback controller 159 adjusts the optical path length of the fiber stretcher 180 as described below according to the phase difference detected by the phase difference meter.

FIG. 3 (A) shows the phase change between the intensity signal of the reference light orbiting the fiber ring and the drive signal of the KTN optical deflector, and FIG. 3 (B) shows the phase difference Δφ and the optical path length of the fiber ring. Show the relationship. The curve a shown by the solid line represents the intensity signal of the reference light, and the curve b shown by the broken line represents the drive signal. The phase difference Δφ (= φ _{a −} φ _b ) between the phase φ _a of the curve _a and the phase φ _{b of the} curve b is such that the optical path length of the ring resonator including the optical delay fiber 170 is the optical coupler 160 under a predetermined temperature. The value taken when the intensity of the output light output from is maximum or a predetermined value, for example, the optical path length L _O at which the coherence length of the output light is maximum is defined as the reference value Δφ _R.

When the optical path length of the fiber ring including the optical delay fiber 170 changes due to a temperature change, the phase of the curve a representing the intensity signal of the reference light changes and the phase difference Δφ takes a value other than the reference value Δφ _R. When the phase difference Δφ is smaller than the reference value (when the reference value is Δφ _R , Δφ <Δφ _R ), the optical path length of the fiber ring becomes shorter and the orbital period becomes shorter as shown in FIG. 3 (B). Therefore, the optical path length of the fiber stretcher 180 is extended and lengthened so that Δφ becomes the reference value Δφ _R. On the other hand, when the phase difference Δφ becomes larger than the reference value (Δφ> Δφ _R ), it means that the optical path length of the fiber ring is long and the orbital period is long as shown in FIG. 3 (B). , The optical path length of the fiber stretcher 180 is shortened and shortened so that Δφ becomes the reference value Δφ _R. In this way, the feedback controller 159 controls the fiber stretcher 180 so that the phase difference Δφ is maintained at the reference value Δφ _R at which the output light grasped in advance is in a desired state.

In this way, by adjusting the optical path length of the fiber stretcher 180, that is, the optical path length of the fiber ring according to the value of the phase difference Δφ, the circumferential period of the ring resonator and the sweep period of the wavelength filter can be multiplied by 1 or more. The difference between the two can be controlled so that the intensity of the output light output from the optical coupler 160 becomes the maximum or a predetermined value.

Here, a little description will be added about adjusting the intensity of the output light output from the optical coupler 250 so that it becomes the maximum or a predetermined value.

In FDML, when the sweep cycle is gradually changed, the intensity of the output light changes dramatically with the sweep cycle in which the time obtained by an integral multiple of 1 or more of the sweep cycle and the orbital time of the resonator match. Further, the output light will be described in detail. If the period is slightly short, the output light intensity is large, if the period is slightly long, the output light is small, and if the periods match, the output light intensity is in the middle. The longest coherence length is when an integral multiple of 1 or more of the sweep cycle matches the orbital time of the resonator. Therefore, the output light intensity at which the coherence length is the longest is measured in advance, and the intensity is targeted. As a value, the coherence length can be maintained at the longest state by adjusting or controlling the sweep cycle. Since the output light intensity that maximizes the coherence length differs for each resonator, it is necessary to measure it in advance for each resonator.

In the above, the output light intensity itself was set as the target value, but instead, the output light intensity divided by the time integral value of the output light intensity during one sweep (standardized) can also be used as the target value. good. In this case, even if the light intensity output from the optical coupler 260 fluctuates due to some influence (such as a change in birefringence due to a change in the tightening strength of the optical fiber to the bobbin due to a temperature change), the target value is reached. Since fluctuations are suppressed, it is possible to withstand environmental changes such as temperature.

On the other hand, if it is necessary to maintain the maximum output light intensity or the output light intensity desired by the user, the sweep cycle is adjusted or controlled so as to have such power.

As a method of adjusting the sweep cycle so as to obtain a predetermined output light intensity, such as setting the output light intensity to the output light intensity that maximizes the coherence length or setting the output light intensity to the output light intensity desired by the user, for example, PID ( Proportional-Integral-Differential) control can be considered. In this case, the target value is a predetermined output light intensity, the manipulated variable is the sweep cycle (frequency), and the controlled variable is the output light intensity.

As a method of adjusting the sweep cycle to maintain the maximum output light intensity, 1) obtain the output light intensity when the cycle is changed within a predetermined range centered on the current sweep cycle, and 2) of which There is a method in which a period having a large light intensity is selected, and then 1) and 2) are repeated many times around the period until the light intensity becomes maximum (or maximum). The parameters of this adjustment method include the initial value of the sweep cycle and the range of the cycle to be changed around the current sweep cycle. When the sweep cycle is discretely changed at equal intervals, the cycle interval is also set as a parameter.

The FDML laser unit is not limited to the configuration shown in FIG. 1, and may have another embodiment as shown in FIG. 2, for example. In the aspect shown in FIG. 2, the wavelength filter 130 has a Littmann arrangement in which a total reflection mirror 223 is further added instead of the litrow arrangement. Further, the ring fiber including the optical delay fiber 170 is a normal optical fiber having no polarization holding function instead of the PM fiber, and is modulated by using a polarization controller 210, a half-wave plate 221 and a polarization beam splitter 222. It is configured to maintain the polarization state of the light propagating in the vessel. The stabilization mechanism 150 of the first embodiment functions in the same manner regardless of which of the wavelength filters 130 and the polarization holding mechanism shown in FIGS. 1 and 2 is used.

(Embodiment 2)
FIG. 4 shows a configuration example of the wavelength sweep light source according to the second embodiment of the present invention. The configuration of the FDML laser unit is the same as that of the first embodiment, and the only difference from the first embodiment is the stabilization mechanism 190. The stabilization mechanism 190 of the second embodiment includes a laser light source 191 that outputs reference light, an intensity modulator 192 that modulates the intensity of reference light, an optical coupler 193 that combines light propagating in a fiber ring and reference light, and a fiber ring. Optical coupler 194 that demultiplexes the reference light from the light propagating in the fiber ring, photodetector 195 that detects the intensity of the reference light that orbits the fiber ring, delay line 196, the intensity signal of the reference light that orbits the fiber ring, and KTN optical deflector 133. A phase difference meter 197 for measuring a phase change with the drive signal of the above is provided.

The stabilization mechanism 190 installs optical couplers 193 and 194 near the input / output ends of the optical delay fiber 170, and transfers the reference light output from the laser light source 191 and modulated by the optical intensity modulator 192 from the optical coupler 193 to the fiber ring. The reference light that has been input and propagated through the optical delay fiber 170 is branched by the optical coupler 194 and detected by the photodetector 195. The feedback controller 198 adjusts the optical path length of the fiber stretcher 180, that is, the optical path length of the fiber ring, based on the phase difference Δφ between the intensity signal of the reference light measured by the phase difference meter 197 and the drive signal of the KTN optical deflector 133. .. Similar to the first embodiment, when the phase difference Δφ is negative (Δφ <0 when the reference value is zero), the optical path length of the optical delay fiber 170 is shortened, that is, the optical path length of the fiber ring is shortened and the orbit time is shortened. Since this means that the optical path length of the fiber stretcher 180 is extended and lengthened so that Δφ becomes zero. On the other hand, when the phase difference Δφ is positive (Δφ> 0 when the reference value is zero), the optical path length of the optical delay fiber 170 becomes long, that is, the optical path length of the fiber ring becomes long and the circuit time becomes long. In order to mean that, the optical path length of the fiber stretcher 180 is shortened and shortened so that Δφ becomes zero. In this way, by adjusting the optical path length of the fiber stretcher 180, that is, the optical path length of the fiber ring according to the value of the phase difference Δφ, the circumferential period of the ring resonator and the sweep period of the wavelength filter can be determined as in the first embodiment. It is possible to control the difference from an integral multiple of 1 or more and adjust so that the intensity of the output light output from the optical coupler 160 becomes the maximum or a predetermined value, for example, the coherence length of the output light becomes the maximum. it can.

Further, as shown in FIG. 2, the wavelength filter 130 may have a Littmann arrangement in which a total reflection mirror 223 is further added instead of the litrow arrangement. Further, the ring fiber including the optical delay fiber 170 is a normal optical fiber having no polarization holding function instead of the PM fiber, and the polarization controller 210, the half-wave plate 221 and the polarization are similar to the configuration shown in FIG. By using the beam splitter 222, the polarization state of the light propagating in the modulator may be maintained.

In the first and second embodiments, an example in which a ring resonator type configuration is used for the FDML laser unit is shown, but in the present invention, the FDML laser unit has a configuration using a wavelength filter including an optical deflector and a diffraction grating. The configuration may be other than the ring resonator type. Further, the intensity modulators 152 and 192 are unnecessary when the laser light sources 151 and 191 are directly modulated. The configuration including the polarizing beam splitter 153 and the quarter wave plate 154 can be replaced by a beam sampler and an isolator. Further, as the signals input to the intensity modulators 152 and 192 and the phase difference meters 158 and 197, the drive signal of the driver device 140 may be used as it is, or a signal obtained by multiplying the drive signal by an integer or a drive signal or an integer thereof. It may be a spike wave in which the double signal and the peak position match.

In the first and second embodiments, the fiber stretcher 180 is used as a means for adjusting the optical path length, but a delay path using a piezo element instead of the fiber stretcher, a variable refractive index waveguide, a delay path of the spatial optical system, and a temperature change It is also possible to use a variable delay path or the like.

110 Isolator 120 Optical amplifier 130 Wavelength filter 131 Circulator 132 Collimeter lens 133 KTN optical deflector 134 Diffraction grid 140 Driver device 160, 193, 194 Optical coupler 170 Optical delay fiber 150, 190 Stabilization mechanism 151, 191 Laser light source 152, 192 Intensity Modulator 153 Polarizing Beam Splitter 154 1/4 Wavelength Board 155 Dicroic Mirror 156, 195 PhotoDetector 157, 196 Delay Line 158, 197 Phase Difference Meter 159, 198 Feedback Controller 180 Fiber Stretcher 210 Polarization Controller 221 Half Wavelength Board 222 Polarized Beam Splitter 223 Total reflector

Claims (6)

An optical amplifier that emits light in a predetermined wavelength band,
Of the light emitted from the optical amplification unit, a wavelength selection unit that changes the selection wavelength at a predetermined wavelength sweep frequency, and a wavelength selection unit.
A first optical branching unit that splits the light output from the wavelength selection unit into two, returns one branched light to the optical amplifiering unit, and outputs the other branched light as output light.
An optical delay unit arranged between the optical amplifier unit and the wavelength selection unit,
An optical path length adjusting unit arranged between the optical amplifier unit and the wavelength selection unit,
A stabilizing mechanism unit that controls the wavelength selection unit so as to adjust the optical path length of the optical path length adjusting unit and the optical path length of the optical path length adjusting unit at least according to a change in the optical path length of the optical path length unit.
A light source unit that outputs reference light intensity-modulated at the wavelength sweep frequency, and
After selecting the wavelength by the wavelength selection unit, the light input to the light delay unit and the reference light are combined, and the reference output from the light delay unit before the wavelength is selected by the wavelength selection unit . An optical demultiplexer that demultiplexes light,
A photodetector that measures the light intensity of the reference light demultiplexed by the photosynthetic demultiplexer
The phase difference between the light intensity signal waveform of the reference light output from the light detection unit and the intensity modulation signal waveform of the light source unit is set to be the phase difference when the output light reaches the maximum or a predetermined value. , A feedback control unit that adjusts the optical path length of the optical path length adjusting unit ,
A wavelength sweeping light source characterized by having a stabilization mechanism including. The optical demultiplexing unit includes a dichroic mirror that reflects light having a wavelength of the reference light and does not reflect light having a wavelength of light emitted from the optical amplifier unit.
The stabilization mechanism includes a polarizing beam splitter and a quarter wave plate.
The reference light immediately after being output from the light source unit is linearly polarized light.
The polarization beam splitter transmits the reference light immediately after being output from the light source unit, and emits light having a polarization axis rotated by 90 degrees with respect to the polarization axis of the reference light immediately after being output from the light source unit. Arranged to reflect,
The reference light output from the light source unit is transmitted through the polarization beam splitter, converted into circularly polarized light through the quarter wave plate, and then combined at the optical demultiplexing unit.
The reference light demultiplexed by the optical demultiplexing unit becomes a polarization axis rotated by 90 degrees with respect to the polarization axis of the reference light immediately after being output from the light source unit on the 1/4 wave plate. After being linearly polarized, it is reflected by the polarized beam splitter and incident on the light detection unit.
The wavelength sweep light source according to claim 1. The optical demultiplexing unit includes a dichroic mirror that reflects light having a wavelength of the reference light and does not reflect light having a wavelength of light emitted from the optical amplifier unit.
The stabilization mechanism includes an isolator and a beam sampler.
The reference light output from the light source unit is transmitted in the order of the isolator and the beam sampler, and then combined at the optical demultiplexing unit.
The reference light demultiplexed by the optical demultiplexing unit is partially reflected by the beam sampler and incident on the photodetector.
The reference light transmitted through the beam sampler is prevented from being incident on the light source portion by the isolator.
The wavelength sweep light source according to claim 1. The feedback control unit shortens the optical path length of the optical path length adjusting unit when the light intensity signal waveform of the reference light is delayed in time with respect to the intensity modulated signal waveform of the light source unit, and the light of the reference light. Increasing the length of the optical path length of the optical path length adjusting unit when the intensity signal waveform is advanced in time with respect to the intensity modulation signal waveform of the light source unit
Wavelength-swept light source according to any one of claims 1 to 3, characterized and this. The reference light, that have a frequency that does not enter the amplification band of the optical amplifying section
Wavelength-swept light source according to any one of claims 1-4, characterized and this. Said wavelength selection section, including a KTN optical deflector and a diffraction grating
Wavelength-swept light source according to any one of claims 1-5, characterized and this.

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