JP7309142B2 - Optical waveguide device, optical module, laser device, and method for manufacturing optical waveguide device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical waveguide device, an optical module, a laser device, and a method for manufacturing an optical waveguide device to which a nanocarbon material is added.

Mode-locked ultrashort pulse lasers are applied to a wide range of fields, such as observation of ultrafast phenomena inside materials and generation of supercontinuum light. Ultrashort pulse lasers are also expected to be applied to next-generation ultrafast optical communications. Especially in recent years, with the rapid increase in the amount of information communication, the power consumption of electrical processing circuits continues to increase, and optical communication requires conversion between light and electricity. Low power consumption is also required for lasers used for wavelength conversion, optical clock generation, and the like.

Active mode-locking devices using modulators require an external power supply and are expensive, so passive mode-locking using nonlinear optical effects has become mainstream. In recent years, carbon nanotubes (CNT), which are excellent in nonlinearity, are expected as saturable absorbers in passive mode-locked femtosecond lasers.

As an application of CNTs to photonics devices, a technique of forming a CNT thin film on the polished surface of a D-shaped optical fiber by a spray method is known (see, for example, Non-Patent Document 1). A method has also been proposed in which a quartz single-mode fiber is stretched under tension, and the constricted waist portion or tapered portion is coated with a polymer containing carbon nanotubes (see, for example, Non-Patent Document 2). Furthermore, a technique has been proposed in which a needle is pierced into a clad layer in which CNTs are dispersed in the clad monomer by ultrasonic agitation, and the needle is scanned while ejecting the core monomer to form a waveguide pattern (for example, non See Patent Document 3). This method is called needle scanning method or mosquito method.

"Ultrashort Pulse Fiber Laser Using Carbon Nanotubes", Laser Research, November 2010, pp.882-888 "Nonlinear optical device using carbon nanotube polymer composite", IEICE Technical Report, OME2011-6 OPE2011-135(2011-11) "Carbon nanotube-doped polymer optical waveguides for passive mode-locked devices", IEICE Technical Report, OCS2015-101, OFT2015-60, OPE2015-220(2016-02)

CNT coating on D-shaped optical fiber has insufficient mechanical strength. In the method of coating the elongated portion of the quartz fiber with CNTs, it is difficult to accurately control the diameter, length, CNT film thickness, etc. of the elongated portion, resulting in low reproducibility. The method of forming a waveguide by injecting a core material into a clad monomer in which CNTs are dispersed using a needle is excellent in mechanical strength. However, the inventors of the present application have found that the reproducibility deteriorates depending on the dispersion state of the cores.

As shown in FIG. 1, the presence of CNT aggregates in the cladding monomers meanders the core and reduces the output power in some channels. Core formation is controlled by the needle scanning program and is affected by pressure, viscosity, etc. around the needle. In particular, when CNT aggregates are present on the trajectory of the needle, the core meanders because the needle is scanned so as to avoid the CNT aggregates, as shown in FIG. A meandering channel introduces excess loss and makes mode-locking difficult.

SUMMARY OF THE INVENTION An object of the present invention is to realize a technique for stably and highly efficiently generating pulsed light by mode-locking with good reproducibility.

In order to achieve the above object, the dispersion of the nanocarbon material in the monomer that is the material of the optical waveguide device is improved.

In a first aspect of the invention, an optical waveguide device comprises:
a cladding layer formed of a first monomer containing a predetermined amount of nanocarbon material and a dispersion stabilizer for the nanocarbon material;
a waveguide core formed of a second monomer different from the first monomer;
have

In a second aspect, the optical waveguide device comprises:
a clad layer formed of a first monomer;
a waveguide core formed of a second monomer containing a predetermined amount of a nanocarbon material and a dispersion stabilizer for the nanocarbon material;
have

By using the above configuration, it is possible to stably and highly efficiently generate pulsed light by mode-locking with good reproducibility.

FIG. 4 is a diagram showing meandering of the core due to CNT aggregation. FIG. 4 is a diagram showing the waveguide state of the optical waveguide device of the first embodiment in comparison with the conventional configuration; It is a figure which compares the nanocarbon addition waveguide of 1st Embodiment with a conventional structure. It is a figure which compares the nanocarbon addition waveguide of 1st Embodiment with a conventional structure. 5 is a diagram comparing the insertion loss of the nanocarbon-doped waveguides of FIG. 4; FIG. FIG. 4 is a cross-sectional view of waveguides produced by changing the amount of nanocarbon material and dispersion stabilizer added to the clad. 4A to 4C are manufacturing process diagrams of the optical waveguide device of the first embodiment; 4A to 4C are manufacturing process diagrams of the optical waveguide device of the first embodiment; 4A to 4C are manufacturing process diagrams of the optical waveguide device of the first embodiment; 4A to 4C are manufacturing process diagrams of the optical waveguide device of the first embodiment; 4A to 4C are manufacturing process diagrams of the optical waveguide device of the first embodiment; 1 is a schematic diagram of a laser device using the optical waveguide device of the first embodiment; FIG. FIG. 9 is a cross-sectional view of a channel of an optical waveguide device used in the laser device of FIG. 8; It is an output waveform of the laser device of the first embodiment. 4 is an output spectrum of the laser device of the first embodiment; It is a manufacturing process drawing of the optical waveguide device of 2nd Embodiment. FIG. 4 illustrates the difference in interaction between a device with a CNT-doped core and a device with a CNT-doped clad. FIG. 4 is a schematic diagram of a laser device using the optical waveguide device of the second embodiment; 8 is an optical microscopic image showing the channel state of the optical waveguide device of the second embodiment; It is an output waveform of the laser device of the second embodiment. It is an output spectrum of the laser device of the third embodiment. It is a loss spectrum when the input light intensity is changed. It is a loss spectrum when the input light intensity is changed. It is a loss spectrum when the input light intensity is changed. It is a figure which shows the relationship between CNT density|concentration and pulse width. It is a figure explaining pulse compression by a nonlinear optical effect. FIG. 4 is a diagram showing peak power characteristics of a laser device; FIG. 4 is a diagram showing the relationship between CNT concentration and threshold current; It is a figure explaining the relationship between excitation light and an output. It is a figure explaining the relationship between excitation light and an output. It is a figure which shows modularization of an optical waveguide device and an optical fiber. FIG. 26 is a schematic diagram of a laser device using the module of FIG. 25; 27 is an output waveform of the laser device of FIG. 26; 27 is an output spectrum of the laser device of FIG. 26;

In embodiments, an appropriate amount of a dispersion stabilizer is added to at least one of the core material and the clad material together with a nanocarbon material such as CNT or graphene when forming a polymer optical waveguide. This realizes uniform dispersion and enables generation of pulsed light with good reproducibility, stability and high efficiency.

By adding a dispersion stabilizer together with the nanocarbon material to the clad monomer constituting the optical waveguide device, aggregation of the nanocarbon in the clad can be suppressed and the waveguide core can be stably formed. By adding a nanocarbon material and a dispersion stabilizer to the core monomer, desired pulse design can be achieved in addition to the effect of suppressing aggregation. An "optical waveguide device" is an optical component in which an optical waveguide is formed. In the present invention, an optical waveguide device can be effectively used as a saturable absorber or nonlinear optical component. Specific embodiments are described below.

<First embodiment>
In the first embodiment, a nanocarbon material and a dispersion stabilizer are added to the clad monomer. Dimethylformamide (DMF), N-methylpyrrolidone (NMP), benzylbenzoate (BEN), and the like can be used as the dispersion stabilizer for the nanocarbon material.

FIG. 2 is an optical microscope image showing the waveguide state of the optical waveguide device of the first embodiment in comparison with the conventional configuration. FIG. 2A shows a waveguide in which only CNTs, which are nanocarbon materials, are added to the clad monomer, and FIG. 2B shows a waveguide in which DMF, a dispersion stabilizer, is added to the clad monomer together with CNTs.

In FIG. 2A, as the clad monomer, an organic-inorganic hybrid resin NP-210 (refractive index 1.559) manufactured by Nissan Chemical Co., Ltd. is used, and 50 ppm of CNT is added to the mass of the clad monomer. there is In FIG. 2(B), the same amount of CNT as in FIG. 2(A) was added, and 2.0 wt. % DMF is added.

In both FIGS. 2A and 2B, the core monomer material is an organic/inorganic hybrid resin NP-005 (refractive index 1.576) manufactured by Nissan Chemical Industries, Ltd. FIG. The core is formed by a known needle scanning method or mosquito method at a scanning speed and an ejection pressure designed to obtain a core diameter of about 10 μm.

In the waveguide to which DMF was not added in FIG. 2(A), CNT aggregates of about 50 μm were scattered in the top view, whereas in the waveguide to which DMF was added in FIG. The existence of aggregates is suppressed, and the size of aggregates is also reduced to 10 μm or less.

Looking at the cross-sectional view, the core of the waveguide not doped with DMF in FIG. 2(A) appears blurred. This is probably because light scattering in the CNT aggregates and meandering of the core reduced the intensity of light emitted from the core, resulting in a decrease in contrast. On the other hand, in the DMF-doped waveguide shown in FIG. 2B, a circular core with a diameter of about 10 μm is maintained. Addition of DMF did not affect the core shape, and an effect of suppressing CNT aggregates was obtained.

FIG. 3 shows optical microscopic images of clad layers prepared by varying the concentration of CNTs and the amount of DMF added. The same clad monomer as in FIG. 2 is used, and 40 ppm of CNTs are added to the mass of the clad monomer in this example. In FIG. 3(B), the same amount of CNT as in FIG. 3(A) was added, and 3.2 wt. % DMF is added.

In FIG. 3(A), CNT aggregates with a size exceeding 50 μm are scattered, whereas in FIG. , has been reduced to a size of 10 μm or less.

FIG. 4 is an optical microscope image of still another optical waveguide fabricated by varying the concentration of CNTs and the amount of DMF added. In FIG. 4(A), the same clad monomer as in FIGS. 2 and 3 was used, 25 ppm of CNTs were added to the mass of the clad monomer, and 0.7 wt. % DMF is added. In FIG. 4(B), 25 ppm of CNTs are added without adding DMF.

In FIG. 4(A), the cross section of the core with a diameter of 10 μm is clearly observed, whereas in FIG. 4(B) the contrast is reduced and the core appears blurred.

FIG. 5 is a diagram comparing the insertion loss of the two optical waveguides produced in FIG. The horizontal axis is exposure waiting time (seconds), and the vertical axis is insertion loss (dB). The longer the waiting time for exposure, the earlier the order of forming the waveguide core by needle scanning, and the shorter the waiting time for exposure, the later the order of forming the core. Each data point along the horizontal axis may be translated into its adjacent channel number.

A laser beam is injected through a single-mode fiber from one end of the 8-channel optical waveguide core produced in FIG. 4, and the output light from the other end of the core is measured with a power meter. The waveguide length of each channel is 1.5 cm.

In the DMF-doped optical waveguide, the insertion loss does not increase so much even after the exposure waiting time elapses, and the loss variation between adjacent channels is small. On the other hand, in an optical waveguide without DMF addition, not only does the insertion loss increase as the exposure waiting time elapses, but also the loss variation between adjacent channels is large.

It is considered that this is because the meandering state of the core and the degree of light absorption and light scattering differ depending on the channel under the influence of CNT aggregates. 0.7 wt. % DMF effectively suppresses CNT aggregation.

FIG. 6 is an optical microscope image of still another optical waveguide fabricated by varying the concentration of CNTs and the amount of DMF added. Using the same clad monomer as in FIGS. 2 to 4, adding 10 ppm of CNT to the mass of the clad monomer, 0.7 wt. % DMF is added. The needle scanning conditions are the same as in FIG.

Even when the amount of CNTs added is 10 ppm, the core diameter is maintained at about 10 μm in each channel. When the insertion loss of these three channels was measured with a waveguide length of 1.8 cm, they were 5.44 dB, 5.94 dB, and 6.66 dB, respectively. is obtained. When these channels are cut to a waveguide length of 1.2 cm and the insertion loss is measured, it is 5 dB or less.

From FIGS. 2 to 6, it can be seen that by adding appropriate amounts of CNTs and a dispersion stabilizer to the clad monomer, CNT aggregation is suppressed, the core arrangement shape is well maintained, and optical loss is suppressed.

The amount of nanocarbon material added is, for example, 10 ppm to 100 ppm with respect to the mass of the clad monomer. If the amount of the nanocarbon material is too large, the nanocarbon material becomes semi-solid and difficult to disperse even if the dispersion stabilizer is added. If the amount of carbon nanomaterial is too low, the desired saturable absorption properties or nonlinearity will not be obtained. Addition of 10 ppm to 100 ppm of nanocarbon material to the cladding monomer is desirable as the amount provides sufficient saturable absorption properties or nonlinearity and can be dispersed in the monomer.

The amount of dispersion stabilizer added is, for example, 0.5 wt. % to 5.0 wt. %. The dispersion stabilizer is an impurity in the cladding monomer, and excessive loss may occur if the amount added is too large. On the other hand, if the amount of dispersion stabilizer added is too large, the viscosity of the clad will decrease, affecting the affinity between the core and the clad. If the amount of the dispersion stabilizer is too small, the CNTs cannot be sufficiently dispersed, and the anti-agglomeration effect cannot be expected. As a range that suppresses aggregation of CNTs and does not affect excessive loss or affect the core, 0.5 wt. % to 5.0 wt. % dispersion stabilizer.

An optical waveguide device formed of a nanocarbon material and a clad material doped with a dispersion stabilizer can be used as a saturable absorber or a mode-locking device.

7A to 7E are manufacturing process diagrams of the optical waveguide device of the first embodiment. First, in FIG. 7A, a nanocarbon-added clad monomer 20 is prepared to form a clad layer. The nanocarbon-added clad monomer 20 is produced by ultrasonically stirring a mixture of a monomer having a predetermined refractive index, a nanocarbon material and a dispersion stabilizer for 2 to 3 hours.

The produced nanocarbon-added clad monomer 20 is poured into a frame 102 formed on a substrate 101, and the surface is flattened using a glass plate or the like as necessary. The frame 102 is formed of, for example, a 500 μm thick silicone sheet and forms an area of 1 cm×10 cm. The clad monomer poured into the frame 102 is allowed to stand on a flat place for about 1 hour.

In FIG. 7B, syringe 41 is filled with core monomer 30 and needle 42 is inserted into cladding layer 21 within frame 102 . The core monomer 30 is made of a monomer having a higher refractive index than the clad layer 21 after curing. In the first embodiment, no nanocarbon material is added to core monomer 30 .

In FIG. 7C, the waveguide core 31 is formed by horizontally scanning the needle 42 while ejecting the core monomer 30 from the tip of the needle 42 . A plurality of waveguide cores 31 may be formed according to the number of channels. The diameter of the waveguide core 31 can be controlled by the inner diameter of the needle 42, scanning speed, discharge pressure, and the like.

In FIG. 7D, UV exposure is performed to polymerize and cure the core and cladding monomers.

In FIG. 7E, the frame 102 on the substrate 101 is removed, and the polymer waveguide is separated from the substrate 101 with a blade or the like. Post-bake for 20 minutes in a 150° air bath to even out stress and fully cure. As a result, the optical waveguide device 10 in which the waveguide core 31 is formed in the nanocarbon-doped clad 25 is obtained. If necessary, the end face of the waveguide core 31 may be exposed by cutting off both ends of the clad in the optical axis direction.

In the optical waveguide device 10, the aggregation in the nanocarbon-added clad 25 is suppressed, and the arrangement shape of the core is well maintained. Excess loss due to core meandering is suppressed, and mode-locking can be achieved with high reproducibility.

FIG. 8 is a schematic diagram of a laser device 1A to which the optical waveguide device 10 of the first embodiment is applied. The laser device 1A is a ring resonator type passive mode-locked fiber laser. Optical waveguide device 10 is used as a passive modelocked device or saturable absorber.

A 980 nm band laser light source, for example, is used as the excitation light source 2, and a silica-based erbium-doped optical fiber (EDF) 7 is used as a gain medium. Optical waveguide device 10 is inserted directly into the ring resonator together with single mode fiber 6 . The resonator length is, for example, 20m. A polarization controller 5 is inserted to adjust the polarization in the resonator to maintain linear polarization.

Light output from the excitation light source 2 passes through the coupler 3, is amplified by the EDF 7, and circulates in one direction in the ring by the optical isolators 8b and 8b. 90% of the light is fed back into the resonator using the 10/90 coupler 4, and the remaining 10% is taken out as output via the optical isolator 8c.

In the resonator, the amplified high-intensity pumping light is transmitted through the optical waveguide device 10, and the low-intensity light component is absorbed. The optical waveguide device 10 of the embodiment has a fast relaxation time (saturation recovery time) and a wide output spectral range, as will be described later.

FIG. 9 is a channel sectional view of the optical waveguide device 10 used in the laser device 1A. The clad monomer is NP-211 manufactured by Nissan Chemical Co., Ltd., the concentration of CNT is 25 ppm, and the addition ratio of DMF is 1.5 wt. %. The waveguide length is 1.4 cm. Both have a circular cross section with a diameter of 10 μm.

10 is a diagram showing the output waveforms of the two channels of FIG. 9. FIG. A single pulse with a repetition frequency of 10 MHz (period of 100 nanoseconds) is observed in any channel. When the autocorrelation function is calculated by the autocorrelator to estimate the time width of the pulse, the pulse width of channel #1 is 1.47 ps and the pulse width of channel #2 is 1.34 ps.

By using the optical waveguide device 10, mode locking can be obtained between a plurality of channels, and pulse oscillation with a narrow pulse width can be obtained.

FIG. 11 shows the output spectrum of the laser device 1A. A wide output spectrum is obtained in any channel. The FWHM (Fill Width Half Maximum) of channel #1 is 2.0 nm, and the FWHM of channel #2 is 1.9 nm. Such a wide wavelength spectrum is a spectrum peculiar to mode-locking.

As described above, the optical waveguide device 10 of the first embodiment functions as a passive mode-locking device, and can realize the narrow pulse width laser device 1A.

<Second embodiment>
The optical waveguide device 10 of the first embodiment can suppress aggregation of the nanocarbon material in the clad and promote good pulse oscillation. However, depending on the scanning trajectory of the needle, it may be affected by relatively small agglomerates present on the trajectory.

In the second embodiment, a nanocarbon material is added to the core material in order to further improve the reproducibility of pulse oscillation. As in the first embodiment, an appropriate amount of dispersion stabilizer is added to suppress aggregation of the nanocarbon material.

FIG. 12 is a manufacturing process diagram of the optical waveguide device 60 of the second embodiment. In FIG. 12A, a clad layer 61 is formed by pouring a clad monomer into a frame 102 formed on a substrate 101 . In this example, no nanocarbon material was added to the clad monomer. As the cladding monomer, a suitable monomer having a lower refractive index after curing than that of the core can be used. For example, NP-211 manufactured by Nissan Chemical Industries, Ltd. can be used.

Meanwhile, a predetermined amount of nanocarbon material and a dispersion stabilizer are added to the core monomer to produce a nanocarbon-added core monomer 50 . A syringe 41 is filled with the produced nanocarbon-added core monomer 50 , and a needle 42 is inserted into the clad layer 61 in the frame 102 . The nanocarbon-added waveguide core 51 is formed by scanning the needle 42 in the horizontal direction while ejecting the nanocarbon-added core monomer 50 from the tip of the needle 42 . A plurality of nanocarbon-added waveguide cores 51 may be formed according to the number of channels. The diameter of the nanocarbon-added waveguide core 51 can be controlled by the inner diameter of the needle 42, the scanning speed, the discharge pressure, and the like.

In FIG. 12B, the polymer waveguide is separated from the substrate 101 by removing the frame 102 on the substrate 101 after the core monomer and the clad monomer are polymerized and cured by UV exposure. Post-bake for 20 minutes in a 150° air bath to even out stress and fully cure. As a result, an optical waveguide device 60 in which the nanocarbon-added waveguide core 51 is formed in the clad 65 is obtained. If necessary, both ends of the clad may be cut off in the optical axis direction to expose the nanocarbon-doped waveguide core 51 on the end face.

Since the optical waveguide device 60 has the nanocarbon-doped waveguide core 51, it can be mode-locked with high reproducibility. Adding nanocarbon material to the core makes it easier to expose to UV light than adding nanocarbon material to the cladding. Since the core diameter is very small, even if the nanocarbon material is added, the effect of ultraviolet absorption is small, and there is no need to increase the exposure intensity or exposure time. In addition, the degree of freedom in design is high because the width of the addition concentration of the nanocarbon material can be easily changed.

FIG. 13 is a diagram for explaining the difference in interaction between the nanocarbon-doped core optical waveguide device of the second embodiment and the nanocarbon-doped clad optical waveguide device of the first embodiment. In FIG. 13(A), in the core to which the nanocarbon material, for example, CNT is added, the propagating light directly interacts with the CNT. CNTs act as saturable absorbers, transmitting only high intensity light propagating through the core and absorbing low intensity light. This promotes pulse oscillation.

In the nanocarbon material of FIG. 13B, for example, the CNT-added clad, among the CNTs dispersed in the clad, the CNTs existing especially around the core interact with the evanescent light from the core. Saturable absorption occurs around the core to promote pulsation, but FIG. 13A is a more direct interaction, improving the pulsation effect.

FIG. 14 is a schematic diagram of a laser device 1B using the optical waveguide device 60 of the second embodiment. The configuration and operation are the same as those of the laser device 1A of the first embodiment except that the inserted mode-locking device is replaced with an optical waveguide device 60 having a nanocarbon-doped core. The same components are denoted by the same reference numerals, and overlapping descriptions are omitted.

FIG. 15 is an optical microscope image showing the channel state of the optical waveguide device 60 of the second embodiment. Here, 1.9 ppm of CNTs were added relative to the mass of the core monomer, and 4 wt. % DMF is added. The cladding contains no additives and the core shape and size are consistent between adjacent channels (Ch. #1 and Ch. #2).

FIG. 16 shows output waveforms of a laser device 1B using the optical waveguide device of FIG. Mode-locking pulse waves are observed in both channel 1 and channel 2, and mode-locking is obtained with good reproducibility in a plurality of channels.

FIG. 17 shows the output spectrum of the laser device 1B. In both channel 1 and channel 2, the wavelength spectrum is broadened and the FWHM is several nm. This is a wavelength spectrum peculiar to mode-locking.

18A to 18C show loss spectra and input light spectra measured by changing the intensity of input light to the optical waveguide device 60. FIG. The input light intensity in FIG. 18A is 12.6 dBm, the input light intensity in FIG. 18B is 13.0 dBm, and the input light intensity in FIG. 18C is 13.4 dBm.

It can be seen that the higher the intensity of the input light, the smaller the loss, and the more efficient saturable absorption occurs. In FIG. 18C, the width of the region where the loss becomes particularly small is widened, and the potential sum absorption works strongly.

FIG. 19 is a diagram showing the relationship between CNT concentration and pulse width. The CNT concentration is varied from 0.95 ppm, 1.9 ppm, 3.2 ppm, 4.3 ppm and the pulse width (ps) is measured at multiple waveguide lengths.

In the range of CNT concentration from 0.9 ppm to 4.5 ppm, narrow pulse width is achieved, especially when CNT concentration is 2±0.2 ppm.

Pulse width is also affected by core length. A certain length is necessary for the core length in order to obtain interaction between the CNTs in the core and the light.

CNT concentration and core length are parameters related to saturable absorption. Although the CNT concentration more directly affects the pulse width, the pulse width can also be optimized by adjusting the core length.

FIG. 20 is a diagram for explaining pulse compression by nonlinear optical effects. As shown in FIG. 20(B), the optical pulses of higher orders of 2nd order or higher cause pulse compression and peak increase due to nonlinear interference between fundamental pulses. When the dispersion (or pulse broadening) by the optical fiber and the pulse compression by the nonlinear optical effect are balanced, a stable solitary wave propagates through the fiber while maintaining its waveform, as shown in FIG. 20(A). Such high peak power and ultrashort pulse laser light is suitable not only for optical amplification and optical clock generation in high-speed optical communication networks, but also for ultrafine processing.

FIG. 21 is a diagram showing peak power characteristics of the laser device 1B. FIG. 21(A) shows the relationship between pulse width and peak power, and FIG. 21(B) shows the relationship between excitation current and peak power.

In FIG. 21(A), no clear tendency is observed in the relationship between the pulse width determined by the amount of CNTs added and the waveguide length and the peak power. It can be seen from FIG. 21B that the peak power increases as the excitation current increases. Then, as explained in FIG. 19, the CNT concentration and waveguide length are optimized to achieve a narrow pulse width, while the laser light is designed so that the desired output power can be obtained by controlling the excitation current. can do.

FIG. 22 is a diagram showing the relationship between the CNT concentration and the threshold current (injection current to the excitation light source 2) required for mode locking. The threshold current of the laser device 1B is measured by changing the CNT concentration added to the core of the optical waveguide device 60 to 0.95 ppm, 1.9 ppm, 3.2 ppm, and 4.3 ppm. All samples have a cladding material of NP-211, a core material of NP-005, and a waveguide length of 4 cm.

In any sample, mode-locked pulse oscillation can be performed at a low current of less than 100 mA, and the power consumption of the laser device 1B can be reduced. In particular, samples with CNT concentrations of 0.95 ppm and 1.9 ppm achieve low threshold currents of 75 mA or less.

From this, it can be seen that by adding a nanocarbon material and a dispersion stabilizer to the core, a direct interaction between light and CNTs can be generated, and pulse oscillation can be promoted at low power.

23 and 24 are diagrams for explaining the relationship between excitation light and output. In FIG. 23, when the intensity of the excitation light supplied from the excitation light source 2 to the EDF 7 (see FIG. 14) is lower than the threshold current Ith, continuous waves are output without laser oscillation. If the intensity of the excitation light is too strong, multimode oscillation will occur and the output will become unstable. Also, coherence is reduced.

An object of the invention is to make the threshold current Ith as low as possible and widen the range in which single-pulse oscillation can be performed as much as possible, as shown in FIG. By lowering the threshold current Ith, the power consumption of the laser device can be reduced as a whole. Reduction of the threshold current Ith is achieved by optimizing the CNT concentration and the waveguide length as described above.

By lowering the threshold current Ith, the single-pulse oscillation mode region can be expanded. When this region is widened, the peak power can be increased by controlling the excitation current while maintaining the single-pulse oscillation mode. This realizes highly efficient and stable pulse oscillation. Moreover, since the nanocarbon material is added to the core, direct interaction between the nanocarbon material and light can be generated. In addition, reproducibility of mode locking is high between channels.

<Modularization of optical waveguide device>
FIG. 25 is a diagram showing a module configuration of an optical waveguide device and an optical fiber. Both the optical waveguide device 10 of the first embodiment and the optical waveguide device 60 of the second embodiment are suitable for modular construction.

FIG. 25A is a perspective view of the optical module 70. FIG. Fiber The optical module 70 is constructed by fixing the holding substrate 73 and the fiber holding substrate 74 .

The fiber holding substrate 73 holds the optical fiber 75 and is fixed to one end face of the optical waveguide device 10 in the optical axis direction with an optical adhesive 71 . The fiber holding substrate 74 holds the optical fiber 76 and is fixed to the other end face of the optical waveguide device 10 in the optical axis direction with an optical adhesive 72 . The optical fibers 75 and 76 are single-mode fibers that form a ring fiber resonator in the laser device 1A or 1B.

As shown in the cross-sectional view of FIG. 25B, the fiber holding substrate 73 has a V-groove 732 formed in the substrate 731 and a cover 733 that holds down the optical fiber 75 in the V-groove 732 . The fiber holding substrate 74 also has the same configuration. As the substrate 731, a suitable substrate that is easy to process can be used, and a silicone substrate is used as an example.

The end face of the optical fiber 75 and one end face of the waveguide core 31 are aligned by, for example, active alignment, and the end face of the optical fiber 76 and the other end face of the waveguide core 31 are aligned. Bare fibers may be used as the optical fibers 75 and 76 for alignment with the waveguide core 31 .

FIG. 25(C) is an image of the optical module 70 actually manufactured. The ends of the optical fibers 75 and 76 opposite to the optical bonding side may be APC (angled physical contact) polished and held by fiber ferrules or connectors. By fixing the fiber holding substrates 73 and 74 to the optical waveguide device 10 with the optical adhesives 71 and 72 to form a module, handling and assembly are facilitated. As described above, the optical waveguide device 60 may be used to form the optical module 70 .

FIG. 26 is a schematic diagram of a laser device 1C using the optical module 70 of FIG. In the laser device 1C, an optical module 70 is inserted between the optical isolators 8a and 8b. An optical fiber 75 fixed to the optical module 70 is connected to the optical isolator 8a, and an optical fiber 76 is connected to the optical isolator 8b.

In this configuration, connection loss due to misalignment is prevented, and the saturable absorption effect of the optical waveguide device 60 due to the addition of the nanocarbon material can be fully exerted.

Other configurations of the laser device 1C are the same as those of the laser devices 1A and 1B, and overlapping descriptions are omitted.

27 is a diagram showing an output waveform of the laser device of FIG. 26. FIG. Alignment deviation is suppressed, and stable pulse oscillation is obtained.

FIG. 28 is the output spectrum of the laser device of FIG. A wide wavelength spectrum characteristic of mode-locking is obtained.

As described above, by adding an appropriate amount of nanocarbon material and dispersion stabilizer to the cladding or core of a polymer optical waveguide, mode-locking can be achieved with good reproducibility and ultrashort pulses can be stably generated. can be done.

The invention is not limited to the specific embodiments described above. For example, graphene may be used as the nanocarbon material instead of CNT. Graphene may be obtained by using a top-down method of dispersing graphene from graphite or a bottom-up method of growing graphene on a substrate. In the present invention, in order to disperse graphene in the clad or core, among the top-down methods, a solution dispersion method may be used in which graphite is added to an organic solvent such as DMF, NMP, or BEN and ultrasonically stirred. Ultrasonic agitation in an organic solvent eliminates van der Waals forces acting between graphite layers, dispersing graphite and graphene in the solvent. Graphite and graphene may be separated by centrifugation to obtain a graphene dispersion.

The core diameter of the waveguide core is not limited to 10 μm, and a waveguide core of a desired size can be formed by appropriately controlling the inner diameter of the needle, ejection pressure, and scanning speed. From the viewpoint of optical connection with a single mode fiber, the diameter of the waveguide core is desirably about 10 μm, but the core diameter may be tapered toward the connection end. Note that the core diameter means the mode field diameter.

A nanocarbon material may be added to both the core and the clad. In this case, both the direct interaction between the nanocarbon material and the propagating light in the core and the interaction between the evanescent light and the nanocarbon material in the cladding near the core further promote mode-locking pulse oscillation. obtain.

1A, 1B, 1C laser device 2 excitation light source 7 EDF (gain medium)
10, 60 optical waveguide device 20 nanocarbon-added clad monomer 21 clad layer 25 nanocarbon-added clad 31 waveguide core 50 nanocarbon-added core monomer 51 nanocarbon-added waveguide core 65 clad 70 optical modules 73, 74 fiber holding substrate 75, 76 optical fiber

Claims (7)

a clad layer that is a polymer of a first monomer containing a predetermined amount of nanocarbon material and a dispersion stabilizer for the nanocarbon material;
a waveguide core that is a polymer of a second monomer different from the first monomer;
has
The cladding layer is a layer with a predetermined thickness extending in an in-plane direction, and the waveguide core is a circular core with a circular cross section extending inside the cladding layer,
The concentration of the nanocarbon material with respect to the mass of the polymer of the first monomer is 10 ppm to 100 ppm, and the proportion of the dispersion stabilizer is 0.5 wt. % to 5.0 wt. % optical waveguide device. a clad layer formed of a polymer of a first monomer;
a waveguide core formed of a polymer of a second monomer containing a predetermined amount of a nanocarbon material and a dispersion stabilizer for the nanocarbon material;
has
The cladding layer is a layer with a predetermined thickness extending in the in-plane direction, and the waveguide core is a single-mode circular core with a circular cross section extending inside the cladding layer,
The optical waveguide device, wherein the concentration of the nanocarbon material with respect to the mass of the polymer of the second monomer is 0.9ppm to 4.5ppm. An optical waveguide device according to claim 1 or 2;
a first holding substrate holding a first optical fiber optically connected to the waveguide core on one end side of the optical waveguide device;
a second holding substrate holding a second optical fiber optically connected to the waveguide core on the other end side of the optical waveguide device;
and wherein the waveguide core, the first optical fiber and the second optical fiber are adhesively fixed. 4. The optical module according to claim 3, wherein at least one of said first holding substrate and said second holding substrate has a V groove for holding said first optical fiber or said second optical fiber. An optical waveguide device according to claim 1 or 2;
an excitation light source that outputs excitation light;
an optical fiber that inputs the excitation light to the optical waveguide device;
an optical coupler that extracts at least part of the light transmitted through the optical waveguide device to the outside;
A laser device having adding a predetermined amount of a nanocarbon material and a dispersion stabilizer for the nanocarbon material to the first monomer to produce a nanocarbon-added clad monomer;
Forming a clad layer with a predetermined thickness that spreads in the in-plane direction with the nanocarbon-added clad monomer,
inserting a needle into the cladding layer and scanning the needle while ejecting a core monomer different from the first monomer from the tip of the needle to form a circular waveguide core;
The concentration of the nanocarbon material with respect to the mass of the first monomer is 10 ppm to 100 ppm, and the proportion of the dispersion stabilizer is 0.5 wt. % to 5.0 wt. %, and a method for fabricating a nanocarbon-doped optical waveguide device. producing a nanocarbon-loaded core monomer containing a predetermined amount of a nanocarbon material and a dispersion stabilizer for the nanocarbon material;
Forming a clad layer with a predetermined thickness extending in the in-plane direction with a clad monomer different from the nanocarbon-added core monomer,
inserting a needle into the cladding layer and scanning the needle while ejecting the nanocarbon-added core monomer from the tip of the needle to form a single-mode circular core waveguide core;
A method for fabricating a nanocarbon-doped optical waveguide device in which the concentration of the nanocarbon material with respect to the mass of the nanocarbon-doped core monomer is 0.9 ppm to 4.5 ppm.

Images