JP2008046404A - Wavelength filter and short pulse forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain miniaturization of a wavelength filter having a sharp wavelength characteristic by simpler constitution. <P>SOLUTION: The wavelength filter is constituted of a silicon filament optical waveguide 115, a quarter wavelength plate 117 and a polarizer 118. In the wavelength filter, a silicon filament core 102 is formed so that, for example, its cross-sectional shape is a rectangle wherein the length (width) of a lower clad 101 in a plane direction is 460 nm and the length (height) of a plane of the lower clad 101 in a normal direction is 200 nm. Thus the cross-section of the silicon filament core 102 is characteristically formed to be flat and when waveguide length is formed to about 2.2 cm, a filter having transmission wavelength interval Δλ=0.08 nm can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavelength filter used for high-speed optical modulation in optical communication and a short pulse shaping apparatus using the wavelength filter.

  The demand for the signal transmission speed of optical communication is steadily increasing, and a device corresponding to 40 Gbps or 100 Gbps, which is the next generation standard, is required from the current mainstream 10 Gbps. In order to increase the transmission speed, it is necessary to increase the modulation speed on the transmission side and the demodulation speed on the reception side. A receiver having a demodulation speed exceeding 50 Gbps has been put into practical use, but a transmitter having a modulation speed exceeding 40 Gbps is under development.

  Devices for realizing these receivers and transmitters necessary for high-speed transmission include those that perform high-speed modulation with a Mach-Zehnder interferometer using the electro-optic effect of lithium niobate crystals or InGaAsP mixed crystals, and InGaAsP mixed crystals. There are high-speed quenching devices based on the electroabsorption effect of the multiple quantum well structure used. All of them directly modulate an electric signal exceeding 40 Gbps into an optical signal. However, these devices require high-frequency electrical wiring, and there is a limit to miniaturization of the devices. Therefore, in order to obtain a small and inexpensive device having a modulation speed exceeding 40 Gbps, a configuration using no high-frequency electrical wiring is required.

  In order to achieve a configuration that does not use high-frequency electrical wiring, low-speed optical signals may be multiplexed in the time domain rather than being converted into optical signals after being multiplexed into high-speed electrical signals. However, at the time of multiplexing, it is necessary to shorten the optical signal while keeping the bit rate low. Further, in the process of shortening the pulse, it is required to be able to be performed with a simple configuration using only an optical passive element and a small and inexpensive configuration.

  In order to satisfy the above requirements, there is a method in which a modulated optical signal from a low-speed optical modulator having a chirp characteristic is transmitted through a wavelength filter having a steep wavelength characteristic and then time division multiplexed using a delay line.

This method will be briefly described. First, in the low-speed optical signal output from the low-speed optical modulator having chirp characteristics, as shown in FIG. Let B be the moment when the optical signal is ON, and C be the moment when the low-speed optical signal falls. Then, the wavelength λ _{A at A} and the wavelength λ _{C at C} are shifted by ± δλ from the wavelength λ _{B at} B due to the chirp δλ of the low-speed optical modulator having chirp characteristics, and the spectrum is As indicated by the solid line in FIG. When this light is processed by a filter X having a transmittance of 1 at a wavelength λ _A and a wavelength λ _C and a transmittance of 0 at a wavelength λ _B as shown by dotted lines in FIG. As shown in (b), two short pulses corresponding to A and C can be formed. The spectrum at this time is as shown by a solid line in FIG.

The light thus formed into two short pulses is processed by a filter Y having a transmittance of 1 at the wavelength λ _A and a transmittance of 0 at the wavelength λ _C as shown by a dotted line in FIG. Then, the obtained time waveform is as shown in FIG. 6C, and can be formed into a single short pulse. A high-speed optical signal can be formed by time-division multiplexing the thus obtained short pulse optical signal using a delay line. These are simple configurations using only optical passive elements, and according to the above-described method, it is expected that a small-sized optical modulator that forms a short-pulse optical signal can be realized at low cost.

  Note that the low-speed modulator having chirp characteristics may be a conventional optical modulator such as a Mach-Zehnder optical modulator using the electro-optic effect of lithium niobate. The delay line may be a conventional optical waveguide.

  By the way, as a wavelength filter having a steep wavelength characteristic, a multilayer filter, an arrayed waveguide grating, and the like can be considered. However, these devices have a device size of several centimeters or more, and there is a limit to downsizing in a configuration using these. .

  On the other hand, as a method for realizing a wavelength filter by a simple method, there are a method using a plurality of asymmetric Mach-Zehnder interferometers and a method using a combination of an optical waveguide having birefringence, a quarter wavelength plate and a polarizer.

In the method using a plurality of asymmetric Mach-Zehnder interferometers, the difference ΔL between the lengths of the two arms of the Mach-Zehnder waveguide (waveguide length), the wavelength of the propagating light is λ, the group refractive index is _ng , and the transmission wavelength interval of the wavelength filter If Δλ is Δλ, the relationship of the following expression (1) is satisfied.

  As can be seen from the above equation (1), in the method using a plurality of asymmetric Mach-Zehnder interferometers, the transmission wavelength interval Δλ of the wavelength filter can be set by the arm length difference ΔL, but the absolute value of the transmission wavelength must be set. I can't. For this reason, in a method using a plurality of asymmetric Mach-Zehnder interferometers, it is not possible to develop a filter characteristic that transmits an arbitrary wavelength at intervals of Δλ.

In contrast, in a method using a combination of an optical waveguide having birefringence, a quarter-wave plate, and a polarizer, it is possible to arbitrarily set the transmission wavelength and the transmission wavelength interval as described below. is there. In this method, when light having a polarization inclined by 45 ° with respect to the intrinsic polarization plane is incident on an optical waveguide having birefringence, light having a different polarization state is emitted depending on the wavelength of the incident light. A wavelength filter can be realized by inserting a quarter wavelength plate and a polarizer on the side. In this method, the difference between the group index for the two orthogonal polarization [Delta] n _g, when the waveguide length of the optical waveguide having birefringence is L, the following expression between the transmission wavelength interval Δλ of (2) The relationship is satisfied.

  Further, the phase difference between two orthogonal polarizations at the exit end described above varies depending on the wavelength λ, and the polarization state at the exit end is generally elliptically polarized. Here, the transmission wavelength can be determined by adjusting to the linearly polarized wave by the rotation by the quarter wavelength plate and matching the angle between this polarization plane and the transmission plane of the polarizer. Thus, in the method using a combination of an optical waveguide having birefringence, a quarter-wave plate, and a polarizer, the transmission wavelength can be set independently of the transmission wavelength interval Δλ. For example, a wavelength filter using a polarization maintaining optical fiber as an optical waveguide having birefringence has been proposed (see Non-Patent Document 1).

C.Yu, Z.Pan, T.Luo, Y.Wang, L.Christen, AEWillner, "40-GHz RZ and CS-RZ Pulse Generation using a Phase Modulator and PM Fiber", ECOC 2004 Proceedings Vol.3, pp.718-719, (2004). T. Tsuchizawa, K. Yamada, H. Fukuda, T. Watanabe, J. Takahashi, M. Takahashi, T. Shoji, E. Tamechika, S. Itabashi, and H. Morita, "Microphotonics Device Based on Silicon Microfabrication Technology" , IEEE Journal of Selected Topics In Quantum Electronics, Vol.11, No.1, pp.232-240, 2005.

  By the way, the value of Δλ necessary for the short pulse shaping for forming the high-speed optical signal described above is considered as follows. When a low-speed optical signal is an RZ signal of 2.5 Gbps, generally, when a 2.5 Gbps RZ signal is modulated by a chirped Mach-Zehnder optical modulator, the rise time is about 100 ps, and 5 GHz (0. There is a chirp δλ of about 04 nm). Accordingly, a pulse component of 100 ps can be extracted with a filter of Δλ = 0.08 nm that does not transmit light of wavelength λ before modulation and transmits the band of λ + 0.04 nm or λ−0.04 nm.

Conventional polarization maintaining fiber as an optical waveguide having birefringence: If you try to achieve this by using a ([Delta] n _g = 10 about ^-4 Non Patent Document 1), the formula (2) from L = 300 meters approximately Length is required and far from miniaturization. In Non-Patent Document 1, the length of DMF = 25 ps PMF (polarization-maintaining fiber) is not specified, but assuming a typical commercial product beat length of 5 mm, the length of the PMF is 24 m. This value corresponds to 40 GHz and is 192 m when converted to 5 GHz.

  The present invention has been made to solve the above problems, and an object of the present invention is to make it possible to reduce the size of a wavelength filter having a steep wavelength characteristic with a simpler configuration.

  The wavelength filter according to the present invention includes an optical waveguide configured by a core made of silicon having a rectangular cross section orthogonal to the waveguide direction, the light to be filtered satisfying a single mode condition, and the optical waveguide. At least a quarter-wave plate through which the emitted light is transmitted and a polarizer through which the transmitted light is transmitted through the quarter-wave plate, and the light to be filtered is polarized with respect to the intrinsic polarization plane of the optical waveguide Is incident on a state inclined by 45 °. The incident light undergoes polarization rotation in the optical waveguide, is adjusted to linearly polarized light by passing through the quarter-wave plate, and only constant polarization is transmitted by passing through the polarizer.

  Further, a short pulse shaping device according to the present invention is a short pulse shaping device using the wavelength filter, comprising an optical modulator having chirp characteristics, and the modulated light output from the optical modulator is the optical waveguide. It is made to enter into. Short pulse light can be obtained from the pulsed light emitted from the short pulse shaping device.

  As described above, according to the present invention, the intrinsic polarization of this optical waveguide is changed to an optical waveguide that is composed of a silicon core having a rectangular cross section and that guides light to be filtered satisfying a single mode condition. Since the light to be filtered is incident with the polarization inclined by 45 ° with respect to the wavefront, and the light emitted from the optical waveguide is transmitted through the quarter-wave plate and the polarizer, a steep wavelength characteristic is obtained. The excellent effect that the wavelength filter which it has can be reduced more in size with a simpler structure is acquired.

  Embodiments of the present invention will be described below. First, the outline of the present invention will be described. In the present invention, an optical waveguide having a silicon fine wire as a core (silicon fine wire optical waveguide) is used as an optical waveguide having birefringence, and a quarter wavelength plate and a polarizer are combined on the output end side to provide steep wavelength characteristics. A wavelength filter is configured. The light to be filtered is incident (coupled) on the incident end side of the silicon fine wire optical waveguide in a state where the polarization is inclined by 45 ° with respect to the intrinsic polarization plane of the silicon fine wire optical waveguide. In addition, the silicon fine wire optical waveguide satisfies the single mode condition for the light to be filtered.

  This will be described below with reference to the drawings. 1A and 1B are a configuration diagram (a) and a partial cross-sectional view (b) showing a configuration example of a wavelength filter according to a first embodiment of the present invention. In the following, a case where the present invention is applied to a pulse shaping apparatus that shapes a short pulse combined with a low-speed optical modulator having chirp characteristics will be described. 1 includes a light source 111, an input optical fiber 112, a chirped optical modulator 113, an introduction optical fiber 114, a silicon thin-wire optical waveguide 115, an output optical fiber 116, and a quarter wavelength. It consists of a plate 117 and a polarizer 118. The chirped optical modulator 113 is a low-speed optical modulator having chirp characteristics. For example, a conventional optical modulator such as a Mach-Zehnder optical modulator using the electro-optic effect of lithium niobate can be used.

  In FIG. 1A, a wavelength filter is constituted by the silicon thin-wire optical waveguide 115, the quarter-wave plate 117, and the polarizer 118. Among these, as shown in the sectional view of FIG. 1A, the silicon fine wire optical waveguide 115 includes a lower clad 101 made of, for example, silicon oxide, a silicon fine wire core 102 formed thereon, and a lower clad 101. It is composed of an upper clad 103 made of silicon oxide formed so as to cover the silicon fine wire core 102. For example, an SOI (Silicon on Insulator) substrate is used, and this SOI layer is processed by a well-known photolithography technique and etching technique to form the silicon thin wire core 102, and thereafter, by a well-known CVD method or the like. The upper clad 103 may be formed by depositing silicon oxide. In this case, the buried insulating layer becomes the lower clad 101.

  In this first embodiment, the silicon thin-wire optical waveguide 115 has a cross-sectional dimension orthogonal to the waveguide direction of the silicon thin-wire core 102 and a refractive index with the cladding so that the light to be filtered satisfies a single mode condition. The difference is set (designed). The silicon thin wire core 102 has, for example, a cross-sectional shape perpendicular to the waveguide direction having a length (width) of 460 nm in the plane direction of the lower cladding 101 and a length (height) in the normal direction of the plane of the lower cladding 101 of 200 nm. It is formed in a rectangle. Thus, the cross section orthogonal to the waveguide direction of the silicon fine wire core 102 is characterized by being formed in a rectangle (flat). According to the silicon fine wire core 102 (silicon fine wire optical waveguide 115) formed in this way, as will be described below, if the waveguide length is about 2.2 cm, the transmission wavelength interval Δλ = 0. A 08 nm filter can be constructed.

  An example of the operation of the wavelength filter configured as described above will be described. First, light source light having a predetermined wavelength is emitted from the light source 111, and this light source light is incident on the chirped optical modulator 113 through the input optical fiber 112. The light incident on the chirped optical modulator 113 is modulated here, and the modulated light that has been modulated passes through the introduction optical fiber 114 and is coupled to the coupling surface 115a (incident end) of the silicon thin-wire optical waveguide 115. The In the coupling surface 115a, the incident modulated light is coupled such that the plane of polarization is inclined at an angle of 45 ° with respect to the intrinsic polarization plane of the silicon fine wire optical waveguide 115 (silicon fine wire core 102). This may be performed, for example, by rotating the introduction optical fiber 114 about the optical axis. In addition, a half-wave plate is provided between the chirped optical modulator 113 and the silicon fine wire optical waveguide 115, and the polarization plane is adjusted by rotating the half-wave plate about the optical axis. Anyway.

The modulated light coupled (incident) in this way undergoes a different amount of polarization rotation for each wavelength in the silicon thin-wire optical waveguide 115, and passes through the output optical fiber 116 that is optically coupled to the output end 115b. The light is incident on 117 and adjusted to linearly polarized waves having different polarization states for each wavelength. By transmitting the modulated light adjusted to linearly polarized light through the polarizer 118, only constant polarization (set linearly polarized wave component) is transmitted. As a result, a filter that selectively transmits some wavelength components is configured. At this time, the transmission wavelength interval Δλ by the wavelength filter including the silicon fine wire optical waveguide 115, the quarter wavelength plate 117, and the polarizer 118 is determined by the length and birefringence of the silicon fine wire optical waveguide 115. Further, the transmission wavelength λ _n (λ _{n + 1} −λ _n = Δλ, n is an integer) is determined by the angle on the plane of polarization of the linearly polarized light that is transmitted through the polarizer 118.

In other words, _assuming that the wavelength of the light source light emitted from the light source 111 is λ _s and the wavelength change due to the chirp obtained by the chirped optical modulator 113 is δλ, first, silicon is filled so that the transmission wavelength interval Δλ = 2δλ is satisfied. What is necessary is just to set the length and birefringence of the thin optical waveguide 115. Further, the angle of the (linear) polarization direction of the polarizer 118 may be set so as to satisfy the transmission wavelength λ _n = λ _s −δλ. By setting in this way, a filter having a transmission wavelength λ _n = λ _s −δλ + (n−1) Δλ is formed, and the chirp component of the propagating modulated light (the component whose wavelength is changed by the chirp, λ _n = λ _s −δλ and λ _n = λ _s + δλ) can be selectively transmitted, and as a result, a short pulse can be shaped.

  These are similar to the two short pulse shaping described with reference to FIGS. 6 (a), 6 (a ′), and 6 (b), and the silicon thin-wire optical waveguide 115, the quarter-wave plate 117, And the filter X is comprised by the polarizer 118. FIG. In general, the chirped optical modulator 113 has a chirp of ± δλ at the preceding stage (rising) and the succeeding stage (falling) of the output pulse. Therefore, in the above configuration, two short pulses are output from the polarizer 118 for one pulse of modulated light output from the chirped optical modulator 113 and input (optically coupled) to the silicon fine wire optical waveguide 115. It will be.

Here, the silicon fine wire optical waveguide 115 will be described. The silicon fine wire optical waveguide 115 can easily obtain large birefringence by making the cross-sectional shape of the silicon core 102 rectangular, and can increase the difference in group refractive index between two orthogonal polarized waves. By increasing the rectangle and the ratio between the long side and the short side of the cross-section (aspect ratio), it is possible to increase the difference [Delta] n _g of group index for the two orthogonal polarization. Thus, if it is possible to increase the difference [Delta] n _g of group index for the two orthogonal polarization, as is clear from the above equation (2), even short waveguide length L, transmission of the wavelength filter The wavelength interval Δλ can be reduced, and a steeper wavelength filter can be configured.

For example, as shown Example in Table 1 below, the short side of the cross-section 280 nm, the long sides 320nm by using the (aspect ratio 0.875) and the silicon core, the difference [Delta] n _g of group index for the two orthogonal polarization Is 0.070, and in order to construct a filter with Δλ = 0.08 nm, the length L of the optical waveguide is 42.9 cm from the above equation (2). Also, the short side of the cross-section 180 nm, by using the silicon core and the long sides 420 nm (aspect ratio 0.429), the difference [Delta] n _g to configure 1.726, and the filter of [Delta] [lambda] = 0.08 nm is, L 1.7 cm is sufficient, and it is easy to reduce the size. Note that the same applies to the case where the short side is arranged in the plane direction and the long side is arranged in the height direction with respect to the plane of the lower cladding 101.

  Further, as described above, the silicon fine wire optical waveguide is an optical waveguide that can be formed by processing the SOI layer of the SOI substrate into a channel type, and is advantageous for manufacturing a micro optical circuit (see Non-Patent Document 2). . Such silicon thin-wire optical waveguides can be applied to well-known silicon integrated circuit fabrication technology and manufacturing equipment in the manufacturing process, and can be expected to reduce costs by mass production, and provide small and inexpensive devices. Is possible.

  Next, FIG. 2 shows a measurement result of the transmission spectrum in the wavelength filter according to the first embodiment including the silicon fine wire optical waveguide 115, the quarter wavelength plate 117, and the polarizer 118 shown in FIG. As shown in FIG. 2, a transmission wavelength interval of Δλ = 0.08 nm is realized. Moreover, the result of having performed the shaping | molding of the short pulse by the short pulse shaping | molding apparatus of 1st Embodiment is shown in FIG. First, modulated light modulated at 1 Gbps as shown in FIG. 3A is output from the chirped optical modulator 113, and the polarization plane of this modulated light is 45 ° with respect to the intrinsic polarization plane of the silicon thin-wire optical waveguide 115. The optical coupling is performed so that the inclination becomes. As a result, the light transmitted through the polarizer 118 is shaped into a short pulse as shown in FIGS. 3B and 3C. FIG. 3C is an enlarged view of FIG. 3B.

  As shown in FIG. 3C, a short pulse with a pulse width of 100 ps or less is obtained with respect to the pulse width of 1 ns of the incident modulated light (1 Gbps). This indicates that the wavelength filter composed of the silicon fine wire optical waveguide 115, the quarter wavelength plate 117, and the polarizer 118 has a steep filter characteristic. As described above, according to the wavelength filter of the first embodiment including the silicon fine wire optical waveguide 115, the quarter wavelength plate 117, and the polarizer 118 illustrated in FIG. Even in a very short state of 2.2 cm, the desired steep filter characteristics can be obtained as described above. Thus, according to the wavelength filter of the first embodiment whose configuration example is shown in FIG. 1, the wavelength filter having steep wavelength characteristics can be more easily downsized.

  Next, a wavelength filter according to a second embodiment of the present invention will be described. FIG. 4 is a configuration diagram (a) showing a configuration example of a pulse shaping apparatus similar to FIG. 1 using the wavelength filter in the second embodiment of the present invention, a perspective view (b) showing a portion, and a partial cross-sectional view. (C). FIG. 4C shows a cross section taken along line cc of FIG. In the pulse shaping apparatus according to the second embodiment shown in FIG. 4, a tapered waveguide 401 is provided at the coupling surface 115a portion and the emission end 115a portion of the silicon fine wire optical waveguide 115.

  As shown in FIG. 4B, the tapered waveguide 401 is provided so as to be thinner as it approaches the incident end (outgoing end), and is provided so as to cover the silicon thin line tapered core 411 and the upper cladding 103. And an intermediate layer 412 having a refractive index between them. For example, when the intermediate layer 412 is made of silicon oxynitride, the refractive index can be set such that the silicon fine wire taper core 411> the intermediate layer 412> the upper cladding 103.

  In addition, the silicon fine wire taper core 411 is formed continuously and integrally with the silicon fine wire core 102, and is formed so that the width becomes narrower as it approaches the incident end (outgoing end). In other words, the tapered waveguide 401 is formed by tapering the entrance end and the exit end of the silicon fine wire core 102 and inserting the intermediate layer 412 in the taper region. By using the tapered waveguide 401 having such a configuration, as is well known, the efficiency of optical coupling between the introduction optical fiber 114 and the emission optical fiber 116 can be improved.

  Next, a wavelength filter according to a third embodiment of the present invention will be described. FIG. 5 is a configuration diagram illustrating a configuration example of a pulse shaping apparatus using the wavelength filter according to the third embodiment. In the pulse shaping device according to the third embodiment shown in FIG. 5, a wavelength filter is newly added on the output side of the polarizer 118 of the pulse shaping device according to the first embodiment described with reference to FIG. It is a thing. The added wavelength filter is composed of a half-wave plate 501, a silicon fine wire optical waveguide 503, a quarter-wave plate 505, and a polarizer 506. An exit optical fiber 504 is provided on the exit end 503 b side of the silicon fine wire optical waveguide 503, and is optically connected to the quarter wavelength plate 505. The silicon fine wire optical waveguide 503 is formed in the same manner as the silicon fine wire optical waveguide 115 and has a predetermined waveguide length. The quarter wavelength plate 505 and the polarizer 506 are the same as the quarter wavelength plate 117 and the polarizer 118.

  In the wavelength filter shown in FIG. 5, similarly to the wavelength filter shown in FIG. 1, first, light source light having a predetermined wavelength is emitted from the light source 111, and this light source light is transmitted through the input optical fiber 112 to the chirped optical modulator 113. To enter. The light incident on the chirped optical modulator 113 is modulated here, and the modulated light that has been modulated passes through the introduction optical fiber 114 and is coupled to the coupling surface 115 a of the silicon thin-wire optical waveguide 115. In the coupling surface 115 a, the incident modulated light is coupled such that the plane of polarization is inclined at 45 ° with respect to the intrinsic polarization plane of the silicon fine wire optical waveguide 115.

  The modulated light coupled (incident) in this way undergoes a different amount of polarization rotation for each wavelength in the silicon thin-wire optical waveguide 115, and passes through the output optical fiber 116 that is optically coupled to the output end 115b. The light is incident on 117 and adjusted to linearly polarized waves having different polarization states for each wavelength. Thereafter, the modulated light adjusted to the linearly polarized light is transmitted only by the polarizer 118 with a fixed polarization (a set linearly polarized light component), and as a result, a part of the wavelength component in the transmitted polarization state is transmitted. To Penetrate. The light thus polarized and transmitted through 118 is transmitted through the half-wave plate 501, then guided through the relay optical fiber 502, and coupled to the coupling surface 503 a (incident end) of the silicon fine wire optical waveguide 503. The In the coupling surface 503 a, the incident light is coupled with the polarization plane having an inclination of 45 ° with respect to the intrinsic polarization plane of the silicon fine wire optical waveguide 502.

As a result, the modulated light shaped into two short pulses having a wavelength satisfying λ _s ± δλ is emitted from the polarizer 118 and transmitted through the half-wave plate 501, whereby the polarization plane is rotated, and the polarization plane Is adjusted to have an inclination of 45 ° with respect to the intrinsic polarization plane of the silicon fine wire optical waveguide 502. The modulated light incident on the silicon thin-line optical waveguide 503 in this way is subjected to polarization rotation in the silicon thin-line optical waveguide 503 and is emitted from the emission end 503b, and enters the quarter-wave plate 505 through the emission optical fiber 504. And adjusted to linear polarization. Thereafter, the modulated light adjusted to the linearly polarized light is transmitted only by the polarizer 506 with a certain polarization (a set linear polarization component), and as a result, a part of the wavelength component in the transmitted polarization state is transmitted. To Penetrate.

At this time, the transmission wavelength interval Δλ ′ of the added wavelength filter composed of the half-wave plate 501, the silicon thin-line optical waveguide 503, the quarter-wave plate 505, and the polarizer 506 is the silicon thin-line optical waveguide 503. The transmission wavelength λ ′ _n (λ ′ _{n + 1} −λ ′ _n = Δλ ′, where n is an integer) is determined by the set angle of the polarizer 506. Here, if the length and birefringence of the silicon fine wire optical waveguide 503 are set so as to satisfy Δλ ′ = 4δλ, and the angle of the polarizer 506 is set so as to satisfy λ ′ = λ _s −2δλ, Of the two short pulses satisfying λ _s ± δλ of the input modulated light, one short pulse satisfying λ _s −δλ can be transmitted. In the configuration shown in FIG. 5, the tapered waveguide 401 shown in FIG. 4 may be provided at the entrance / exit ends of the silicon fine wire optical waveguide 115 and the silicon fine wire optical waveguide 503.

  In the embodiment described above, the lower clad 101 and the upper clad 103 are made of silicon oxide. However, the present invention is not limited to this, and may be made of silicon oxynitride or silicon nitride. . Further, these clads may be made of polyimide resin, epoxy resin, or the like. In short, it suffices if a waveguide made of a silicon fine wire core is configured. For example, a silicon fine wire core may be formed on a lower clad layer made of silicon oxide, and this may be used as a space. In this case, the space above the lower cladding layer and the silicon fine wire core functions as the upper cladding.

It is the block diagram (a) and the fragmentary sectional view (b) which show the structural example of the wavelength filter in embodiment of this invention. FIG. 6 is a characteristic diagram showing a measurement result of a transmission spectrum in a wavelength filter including the silicon fine wire optical waveguide 115, the quarter wavelength plate 117, and the polarizer 118 shown in FIG. It is a characteristic view which shows the result of having shape | molded the short pulse by the short pulse shaping | molding apparatus which concerns on 1st Embodiment. FIG. 6 is a configuration diagram (a) showing a configuration example of a pulse shaping apparatus similar to FIG. 1 using the wavelength filter in the second embodiment of the present invention, a perspective view (b) showing a portion, and a partial sectional view (c). is there. It is a block diagram which shows the structural example of the pulse shaping apparatus using the wavelength filter in the 3rd Embodiment of this invention. It is explanatory drawing for demonstrating shaping | molding into a short pulse by transmitting the modulated optical signal from the low-speed optical modulator with a chirp characteristic to the wavelength filter with a steep wavelength characteristic.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Lower clad, 102 ... Silicon fine wire core, 103 ... Upper clad, 111 ... Light source, 112 ... Input optical fiber, 113 ... Chirp type optical modulator, 114 ... Introduction optical fiber, 115 ... Silicon fine wire optical waveguide, 115a ... coupling surface, 115b ... emission end, 116 ... emission optical fiber, 117 ... quarter-wave plate, 118 ... polarizer.

Claims (2)

An optical waveguide that is composed of a silicon core having a rectangular cross section orthogonal to the waveguide direction and that guides light to be filtered satisfying a single mode condition;
A quarter-wave plate through which light emitted from the optical waveguide is transmitted;
A polarizer that transmits the transmitted light that passes through the quarter-wave plate;
The wavelength filter is characterized in that the light to be filtered is incident in a state where the polarization is inclined by 45 ° with respect to the intrinsic polarization plane of the optical waveguide. A short pulse shaping device using the wavelength filter according to claim 1,
A short pulse shaping apparatus comprising: an optical modulator having chirp characteristics; and the modulated light output from the optical modulator is incident on the optical waveguide.

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