JP2008046546A - Optical transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter for optical interconnection which can secure a large transmission capacity even if the number of light-emitting elements such as VCSEL is small, and which permits to miniaturize the device easily. <P>SOLUTION: Continuous light of different wavelengths is emitted from N pieces of light emitting elements 111. An optical coupler 115 mixes (multiplexes) those continuous light and supplies them to M pieces of optical waveguides 117. N pieces of modulators 121 are connected to each optical waveguide 117 in series. These N pieces of modulators 121 modulate the light of the respective different wavelengths. Consequently, a WDM light signal of a multiplex degree N for M channels is output in the direction parallel to a surface of a substrate 110 from an optical waveguide array 113. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmitter used for optical interconnection in which electronic devices such as LSI (Large Scale Integrated Circuit) are optically connected to transmit and receive signals, and is particularly applicable to an optical interconnection having a large transmission capacity. The present invention relates to an optical transmitter.

  In an information processing apparatus such as a computer, signals are transmitted and received between electronic devices (such as LSIs) mounted on the same printed circuit board or on different printed circuit boards. In such an interconnection between electronic devices, it is expected that a large transmission capacity (transmission band) as much as 10 Tb / s (terabyte / second) will be required in the future. With such an increase in transmission capacity, it is considered to use light interconnection instead of electrical interconnection using metal wiring such as Cu (copper) which has been generally used conventionally. Yes.

  To realize optical interconnection, an optical transmitter including an E / O (electric / optical) conversion element that converts an electrical signal into an optical signal, and an O / E (optical / optical) that converts the optical signal into an electrical signal. An optical receiver having an (electric) conversion element is required. As the E / O conversion element, for example, the use of a surface emitting laser (Vertical Cavity Surface Emitting Laser: hereinafter referred to as “VCSEL”) having a feature of low cost and low power consumption is being studied. A photodiode or the like can be used as the O / E conversion element.

  Non-Patent Document 1 describes an optical transmitter for optical interconnection having the structure shown in FIG. This optical transmitter includes an LSI 11 mounted on a printed board 10, a plurality of VCSELs 12, and an optical waveguide array 13. In this optical transmitter, a plurality of VCSELs 12 are arranged in the width direction of the printed circuit board 10 (one-dimensional arrangement). Each VCSEL 12 is individually supplied with an electrical signal from the LSI 11, and an optical signal (modulated light) corresponding to the electrical signal is output from each VCSEL 12.

  The optical signals output from these VCSELs 12 are input to, for example, an optical receiver mounted on the same printed circuit board 10 or another printed circuit board through the optical waveguide array 13 and converted into electrical signals. Non-Patent Document 1 describes an optical transmitter that uses 32 VCSELs driven at 10 Gb / s (gigabytes / second) and can secure a transmission capacity of 320 Gb / s in total.

  Non-Patent Document 2 describes an optical transmitter in which VCSELs are two-dimensionally arranged to increase transmission capacity. In this optical transmitter of Non-Patent Document 2, as shown in FIGS. 2A and 2B, (M × N) VCSELs 22 are two-dimensionally arranged on an LSI 21 mounted on a printed circuit board 20. ing. Here, M is the number of VCSELs 22 arranged in the Y direction in FIG. 2B, and N is the number of VCSELs 22 arranged in the X direction. From these VCSELs 22, an optical signal (modulated light) corresponding to the electrical signal supplied from the LSI 21 is output.

  Above the VCSEL 22, a microlens array 23 configured by two-dimensionally arranging (M × N) microlenses corresponding to each VCSEL 22, and an optical signal transmitted through the microlens array 23 is printed on the printed circuit board 20. A 45-degree mirror 24 that reflects in a parallel direction is provided. If the configuration of the optical transmitter described in Non-Patent Document 2 is used, it is possible to realize a transmission capacity of 10 Tb / s by using 1000 VCSELs 22 driven at 10 Gb / s in the future. Possible.

  Non-Patent Document 3 describes an optical transmitter using a wavelength division multiplexing (WDM) transmission technique. Also in this optical transmitter of Non-Patent Document 3, (M × N) VCSELs 32 are two-dimensionally arranged on an LSI 31 mounted on a printed circuit board 30 as shown in FIGS. ing. Here, M is the number of VCSELs 32 arranged in the Y direction in FIG. 3B, and N is the number of VCSELs 32 arranged in the X direction. These VCSELs 32 output an optical signal (modulated light) corresponding to the electrical signal supplied from the LSI 31. In the optical transmitter of Non-Patent Document 3, the wavelengths of light emitted from N VCSELs 32 arranged in the X direction are different from each other.

  Above the VCSEL 32, an optical multiplexer 34 that multiplexes the optical signals output from the N VCSELs 32 arranged in the X direction and outputs the multiplexed optical signals as a WDM optical signal is disposed. On the lower surface side of the optical multiplexer 34, a microlens array 34 a composed of (M × N) microlenses arranged to face each VCSEL 32 is provided. On the upper surface side of the optical multiplexer 34, M microlenses 34 b that collect the WDM optical signal output from the optical multiplexer 34 are arranged side by side in the Y direction. Further, above these microlenses 34b, optical fibers 35 are respectively disposed with their end faces (light incident surfaces) facing the microlenses 34b.

  In the optical transmitter of Non-Patent Document 3 configured as above, the optical signals output from (M × N) VCSELs 32 are input to the optical multiplexer 34 through the microlens array 34a. The optical multiplexer 34 multiplexes the emission lights of the N VCSELs 32 arranged in the X direction to generate M channel WDM optical signals, and outputs the WDM optical signals (spatial parallel WDM optical signals) upward. . The M-channel WDM optical signals output from the optical multiplexer 34 enter the corresponding optical fibers 35 through the microlenses 34b. Then, the light is transmitted through the optical fibers 35 to an optical receiver mounted on the same printed circuit board 30 or another printed circuit board.

  Thus, in the optical transmitter of Non-Patent Document 3, a total of 250 Gb is obtained by generating WDM optical signals for M channels using the optical multiplexer 34 and transmitting these WDM optical signals through M optical fibers. A transmission capacity of / s is realized.

In addition, there exist patent documents 1, 2 and nonpatent literatures 4-7 as a prior art considered to be related to this invention. Patent Document 1 describes the structure of a waveguide type optical modulator. Patent Document 2 describes an optical interconnection circuit between wavelength multiplexing TFT circuits in which a micro tile element having a light emitting function or a light receiving function having wavelength selectivity is electrically connected to a thin film transistor circuit. Further, Non-Patent Documents 4 and 5 describe the structure of an optical coupler, and Non-Patent Documents 6 and 7 describe a modulator composed of a plurality of ring-shaped optical waveguides.
JP 2004-109457 A JP 2004-193144 A 2003 IEICE Electronics Society Conference C-3-123 Electronic Components and Technology Conference, 231page, 2000 IEEE Photonics Technology Letters, vol.17, No.1, 220-222page, 2005 IEEE Photonics Technology Letters, vol. 4, page1032-1035, 1992 IEEE Photonics Technology Letters, vol. 1, page241-243, 1989 IEEE Journal of Lightwave Technology, vol. 24, page2146-2155, 2006 Journal of Applied Physics, vol. 96, page6008-6015, 2004

  The present inventors consider that the optical transmitters described in Non-Patent Documents 1 to 3 described above have the following problems. That is, according to the technique described in Non-Patent Document 1, if a 10 Gb / s drive VCSEL is used to secure a transmission capacity of 10 Tb / s, it is necessary to prepare 1000 VCSELs. However, it is extremely difficult to ensure the reliability of 1000 VCSELs at the same time. In addition, a large space is required to arrange 1000 VCSELs in one direction, which is considered difficult to realize from the viewpoint of mounting density.

  Even in the optical transmitter described in Non-Patent Document 2, in order to secure a transmission capacity of 10 Tb / s using a 10 Gb / s VCSEL, it is necessary to prepare 1000 VCSELs. In the optical transmitter of Non-Patent Document 2, VCSELs are two-dimensionally arranged so that space is acceptable, but it is extremely difficult to ensure the reliability of 1000 VCSELs at the same time as the optical transmitter of Non-Patent Document 1. There is a problem that it is. In addition, there is a problem that a complicated work of aligning the optical axes of 1000 VCSELs and 1000 microlenses is required.

  Furthermore, in the optical transmitter of Non-Patent Document 2, a 45-degree mirror is required to transmit the optical signal output from the VCSEL in a direction parallel to the substrate surface. For this reason, a space for arranging the 45-degree mirror above the printed circuit board is required, and there is a problem that downsizing of the apparatus is hindered.

  Even in the optical transmitter of Non-Patent Document 3, it is necessary to prepare 1000 VCSELs in order to secure a transmission capacity of 10 Tb / s using a 10 Gb / s VCSEL. There is a problem that it is difficult to ensure at the same time. In addition, a complicated operation of aligning the optical axes of 1000 VCSELs and 1000 microlenses is required.

  Furthermore, in the optical transmitter of Non-Patent Document 3, it is necessary to bend the optical fiber at a right angle in order to transmit the optical signal output from the VCSEL in a direction parallel to the surface of the printed circuit board. Similar to the optical transmitter, a space is required above the printed circuit board, and there is a problem that downsizing of the apparatus is hindered.

  An object of the present invention is to provide an optical transmitter for optical interconnection that can secure a large transmission capacity even if the number of light emitting elements such as a VCSEL is small and that can easily reduce the size of the apparatus.

  According to one aspect of the present invention, an optical waveguide to which continuous light is input, and a plurality of optical waveguides that are arranged along the optical waveguide and that modulate light passing through the optical waveguide according to an electric signal supplied from the outside. And an optical signal output unit that outputs light modulated by the plurality of modulators, wherein the plurality of modulators have different wavelengths of light that can be modulated, respectively. Is provided.

  In the optical transmitter of the present invention, a plurality of modulators are arranged along an optical waveguide to which continuous light is supplied, and each of the modulators modulates light of a different wavelength, and a WDM optical signal is converted. Generate. In this case, if the number of modulators is N, the multiplicity of the WDM optical signal is N. This optical signal is output from the end face of the optical waveguide via the optical signal output unit. Therefore, when the optical waveguide is formed parallel to the surface of the support substrate, the optical signal is output in a direction parallel to the surface of the support substrate. For this reason, a mirror or an optical fiber for changing the traveling direction of the optical signal is not necessary, and the apparatus can be miniaturized.

  According to another aspect of the present invention, M (where M is an integer of 2 or more) optical waveguides, a continuous light supply unit that supplies continuous light to each of the M optical waveguides, and the M optical waveguides N modulators (N is an integer of 2 or more) connected in series to each of the optical waveguides, and modulators that modulate light passing through the optical waveguides in response to an electric signal supplied from the outside; An optical signal output unit for outputting light modulated by the N modulators for each of the optical waveguides, and the N modulators connected in series to one optical waveguide can be modulated. An optical transmitter characterized in that the wavelengths of light are different from each other is provided.

  In the optical transmitter of the present invention, M optical waveguides and a continuous light supply unit that supplies continuous light to these optical waveguides are provided. Each optical waveguide is connected in series with N modulators. Therefore, in the optical waveguide of the present invention, a WDM optical signal with N multiplicity is generated for M channels. These optical signals are output in a direction parallel to the surface of the support substrate via the optical signal output unit.

  The continuous light supply unit includes, for example, N light emitting elements that generate continuous light having different wavelengths, and an optical coupler that multiplexes continuous light emitted from the light emitting elements and supplies the light to M optical waveguides. Consists of. With such a configuration, a large transmission capacity can be ensured with a small number of light emitting elements. Further, the number of parts can be reduced, and the apparatus can be further downsized. Furthermore, since the number of places to be optically coupled is reduced, the assembly is facilitated and the reliability is improved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 4 is a perspective view showing an interconnection optical transmitter according to the first embodiment of the present invention, and FIG. 5 is a block diagram showing the configuration of the optical transmitter.

  As shown in FIG. 4, the optical transmitter according to this embodiment includes a printed circuit board (supporting substrate) 110, N light emitting elements (light sources) 111 mounted on the printed circuit board 110, and a modulator integrated element 112. And an optical waveguide array (optical signal output unit) 113 and an LSI 114 flip-chip bonded onto the modulator integrated element 112. On the upper surface of the modulator integrated element 112, an electrode 115 for flip chip bonding to the LSI 114 is provided.

  Further, as shown in FIG. 5, the modulator integrated element 112 includes an optical coupler 115 and a modulator array unit 116, and the modulator array unit 116 has (M × N) wavelength selection functions. The modulator 121 is configured. Here, M is the number of modulators 121 arranged in the Y direction in FIG. 5, and N is the number of modulators 121 arranged in the X direction. In FIG. 5, M = N = 4, but the values of M and N are determined based on the required total transmission capacity and the performance of each element.

  The N light emitting elements 111 generate continuous light having different wavelengths for each light emitting element 111 (that is, unmodulated light). In FIG. 5, four light emitting elements 111 are provided, and the wavelengths of light generated by these light emitting elements 111 are λ1, λ2, λ3, and λ4. In this embodiment, a DFB (Distributed Feed-Back) laser having excellent oscillation wavelength unity is used as these light emitting elements 111. Each light emitting element 111 is optically coupled to an optical coupler 115 of a modulator integrated element 112 as shown in FIG.

  The optical coupler 115 mixes (multiplexes) light having different wavelengths output from the N light emitting elements 111 to generate wavelength multiplexed continuous light. The wavelength multiplexed continuous light is respectively output to M (four in FIG. 5) optical waveguides 117 and transmitted to the modulator array unit 116.

  In the modulator array unit 116, as shown in FIG. 5, N (four in FIG. 5) modulators 121 are connected in series to one optical waveguide 117. These N modulators 121 modulate light of different wavelengths in accordance with the electrical signal supplied from the LSI 114. Here, it is assumed that light with wavelengths λ1, λ2, λ3, and λ4 is modulated in order from the modulator 121 close to the optical coupler 115.

  FIG. 6 is a schematic diagram showing the concept of operation of the modulator 121. FIG. 6 shows a modulator that modulates light of wavelength λ4. As shown in FIG. 6, light passing through the optical waveguide 117 is separated into light of wavelength λ4 and light of other wavelengths λ1, λ2, and λ3 at the input unit 121a. The modulation unit 121b modulates the light having the wavelength λ4 separated by the input unit 121a according to the electric signal supplied from the LSI 114. On the other hand, the lights of wavelengths λ1, λ2, and λ3 separated by the input unit 121a are transmitted to the output unit 121c. The output unit 121c mixes (multiplexes) the light with the wavelength λ4 modulated by the modulation unit 121b and the light with the wavelengths λ1, λ2, and λ3 transmitted from the input unit 121a, and outputs it to the output-side optical waveguide 117. To do. As described above, the modulator 121 modulates only light having a predetermined wavelength out of light passing through the optical waveguide 117, and outputs light having other wavelengths in the same state as when input.

  The optical waveguide array 113 includes M (four in FIG. 5) optical waveguides 113a. These optical waveguides 113 a are optically coupled to the M optical waveguides 117 of the modulator integrated element 112 in a 1: 1 manner. A WDM optical signal is transmitted to the optical receiver mounted on the same printed circuit board 110 or another printed circuit board via the optical waveguide array 113.

  Hereinafter, specific structures of the optical waveguide 117, the optical coupler 115, and the modulator 121 that constitute the modulator integrated element 112 will be described. The optical waveguide 117, the optical coupler 115, and the modulator 121 are all configured with a lower cladding layer, a core layer, and an upper cladding layer formed on a silicon substrate (semiconductor substrate) as basic elements. The optical waveguide 117, the optical coupler 115, and the modulator 121 are integrally formed on the same silicon substrate by using a general film forming method (for example, a CVD method), a photolithography method, and an etching method. Is done.

7A is a cross-sectional view showing the structure of the optical waveguide 117 of the modulator integrated element 112, and FIG. 7B is a diagram for explaining the size of each part of the optical waveguide 117. FIG. As shown in FIG. 7A, an SiO ₂ layer 131 is formed on the silicon substrate 130 as a lower cladding layer. The thickness t1 (see FIG. 7B) of the SiO ₂ layer 131 is, for example, 3.0 μm.

On the SiO ₂ layer 131, an Si layer 132 constituting the core layer is formed. The thickness t2 (refer to FIG. 7B) of the rib-shaped portion (hereinafter referred to as “core 132a”) serving as an optical waveguide in the Si layer 132 is, for example, 250 nm, and the thickness t3 of the other portion of the Si layer 132 (see FIG. 7B). In FIG. 7B, for example, the thickness is 50 nm. The width w1 (see FIG. 7B) of the core 132a is, for example, 450 nm. In this embodiment, as shown in FIG. 7A, the Si layer 132 is also formed thin (thickness t3) on the SiO ₂ layer 131 other than the portion that becomes the optical waveguide. Hereinafter, the thinly formed Si layer 132 is referred to as a Si thin film 132b.

An SiO ₂ layer 133 is formed on the Si layer 132 as an upper clad layer, and the periphery of the core 132a is covered with SiO ₂ layers 131 and 133.

In the optical waveguide 117 configured in this way, the refractive index of the core 132a is higher than the refractive index of the SiO ₂ layers 131 and 133 covering the periphery thereof, so that the light passing through the core 132a is the interface with the SiO ₂ layers 131 and 133. Total reflection. Thereby, the light is confined in the core 132a.

  8A is a top view showing the configuration of the optical coupler 115, and FIG. 8B is a diagram for explaining the size of each part of the optical coupler 115. FIG. FIG. 9 is an enlarged view of a portion surrounded by a broken line A in FIG. The structure of this type of optical coupler is described in Non-Patent Documents 4 and 5 described above.

  As shown in FIG. 8A, the optical coupler 115 is composed of an input port side optical waveguide array 141 composed of N optical waveguides 141a, a slab waveguide section 142, and M optical waveguides 143a. Output port side optical waveguide array 143 and dummy optical waveguides 141b and 143b. These optical waveguides 141a, 141b, 143a, 143b and the slab waveguide portion 142 are constituted by a core layer, and a cladding layer is disposed around the core layer.

  The N optical waveguides 141a constituting the input port side optical waveguide array 141 are optically coupled to the corresponding light emitting elements 111, respectively. The width of the optical waveguide 141a at the input side end face is, for example, 450 nm (same as the width of the optical waveguide 117 in FIG. 7), and the pitch p1 (see FIG. 8B) of the optical waveguide 141a at the input side end face is, for example, 300 μm. . In addition, as shown in FIG. 9, the width of the optical waveguide 141 a becomes wider toward the slab waveguide portion 142 in the range of 50 μm from the slab waveguide portion 142 of the optical waveguide 141 a. The width w2 of the connection portion is set to 0.8 μm, for example, and the pitch p2 is set to 1.0 μm, for example.

  Similarly to the optical waveguide 141a, the M optical waveguides 143a constituting the output port side optical waveguide array 143 are set to have a width of, for example, 450 nm and a pitch of, for example, 300 μm at the output side end face. Further, in the range of 50 μm from the slab waveguide portion 142 of the optical waveguide 143a, the width of the optical waveguide 143a becomes wider as the slab waveguide portion 142 is approached, and the optical waveguide 143a at the connection portion with the slab waveguide portion 142 is obtained. The width is set to 0.8 μm, for example, and the pitch is set to 1.0 μm, for example.

  The shapes of the input side and output side surfaces of the slab waveguide section 142 are defined by a circle having a radius R of, for example, 150 μm, as shown in FIG. Moreover, in order to ensure the uniformity of the wavelength-multiplexed continuous light distributed to each optical waveguide 143a on both sides in the Y direction on the input side and both sides in the Y direction on the output side of the slab waveguide part 142, respectively. A plurality of dummy optical waveguides 141b and 143b are provided.

  FIG. 10 is a top view showing the configuration of the modulator 121. Here, a ring-shaped resonant optical modulator is used as the modulator 121. The structure of this type of ring-shaped resonant optical modulator is described in Non-Patent Documents 6 and 7.

  As shown in FIG. 10, the modulator 121 includes three ring-shaped optical waveguides 151 a, 151 b and 151 c and a drop port 152. The ring-shaped optical waveguides 151a, 151b, and 151c are arranged side by side in the Y direction between the optical waveguide 117 and the drop port 152. The optical waveguide 117 and the ring-shaped optical waveguide 151a, the ring-shaped optical waveguide 151a and the ring-shaped optical waveguide 151b, the ring-shaped optical waveguide 151b and the ring-shaped optical waveguide 151c, and the ring-shaped optical waveguide 151c and the drop port 152 are respectively directional couplers. Is configured. The drop port 152 is composed of an optical waveguide, and the function of radiating the light transferred from the optical waveguide 117 through the directional couplers configured by the ring-shaped optical waveguides 151a, 151b, 151c from both end faces. It has.

  The sizes of the ring-shaped optical waveguides 151a, 151b, and 151c are set according to the wavelength of light to be modulated. For example, in the case of a modulator that modulates light having a wavelength of 1.55 μm, the radii of the ring-shaped optical waveguides 151a, 151b, and 151c are set to 8 μm. The directional coupler configured by the optical waveguide 117 and the ring-shaped optical waveguide 151a and the directional coupler configured by the ring-shaped optical waveguide 151c and the drop port 152 both have a coupling coefficient of 0.137. The directional coupler configured by the ring-shaped optical waveguides 151b and 151c and the directional coupler configured by the ring-shaped optical waveguides 151b and 151c are both coupled. The coefficient is set to 0.00746, and the power transfer rate is set to 0.0056%.

  FIG. 11 is a view showing a cross section of the ring-shaped optical waveguides 151a, 151b, and 151c. As shown in FIG. 11, the basic structure of the ring-shaped optical waveguides 151a, 151b, 151c is the same as that of the optical waveguide 117 shown in FIG. 7A, but conductive impurities are introduced above the core 132a. An electrode 153 made of polysilicon is provided. Further, a conductive impurity is introduced into a part of the Si thin film 132b slightly separated from the core 132a, and the part into which the conductive impurity is introduced serves as a common electrode (ground electrode) 154. These electrodes 153 and 154 are electrically connected to flip-chip connection electrodes (electrodes 115 in FIG. 4) provided above the modulator 121 (the upper surface of the modulator integrated element 112). An LSI 114 is flip-chip connected on the connection electrodes.

  In the modulator 121 configured as described above, when no voltage is applied to the electrode 153, light having wavelengths λ1, λ2, λ3, and λ4 passing through the optical waveguide 117 is directly transmitted from the input port (input unit) to the through port (input port). Output). When a voltage is applied to the electrode 153, only light of a specific wavelength (for example, light of wavelength λ1) is transferred to the drop port 152 via the ring-shaped optical waveguides 151a, 151b, and 151c, and light of other wavelengths (for example, wavelength) λ2, λ3, and λ4 light) are transmitted to the through port. The light transferred to the drop port 152 is radiated from the end of the drop port 152 and dissipated.

12A and 12B are diagrams illustrating the characteristics of the modulator 121. FIG. 12A shows the characteristics when no voltage is applied to the electrode 153 (when the refractive index change Δn = 0 of the optical waveguide), and FIG. 12B shows the characteristics when a voltage is applied to the electrode 153. Is shown. Here, the characteristics of a modulator that modulates light having a wavelength of 1.55 μm are shown. 12A and 12B, the vertical axis indicates the transmittance (unit: dB) to the through port (output unit), and the intensity of light input to the input port (input unit) of the modulator. It is a logarithmic value of the ratio to the intensity of light output to the through port. Here, it is assumed that a change in refractive index of 7 × 10 ⁻⁴ (Δn = 7 × 10 ⁻⁴ ) of the optical waveguide is generated by applying a voltage.

  As shown in FIG. 12A, when no voltage is applied to the electrode 153, the cutoff band of the modulator is located above 1.55 μm (the wavelength is longer). Therefore, light having a wavelength of 1.55 μm passing through the optical waveguide 117 is output to the through port without being attenuated by the modulator. On the other hand, when a voltage is applied to the electrode 153, the center of the cutoff band of the modulator moves to a position of 1.55 μm as shown in FIG. Therefore, light having a wavelength of 1.55 μm passing through the optical waveguide 117 is transferred to the drop port 152 via the ring-shaped optical waveguides 151 a, 151 b, and 151 c and is diffused from both ends of the drop port 152.

  By changing the voltage applied to the electrode 153 with time, light having a wavelength of 1.55 μm passing through the optical waveguide 117 is modulated. In this way, the wavelength multiplexed continuous light output from the optical coupler 115 to the optical waveguide 117 is modulated by the N modulators 121 arranged along the optical waveguide 117, and as a result, from the modulator array unit 116 to the WDM. An optical signal (modulated light) is output.

  In the present embodiment, the arrangement pitch of the optical waveguides 117 in the modulator integrated element 112 is the same as the arrangement pitch of the optical waveguides 143a on the output port side of the optical coupler 115, for example, 300 μm. On the other hand, since the size of the modulator 121 is about several tens of μm, the modulation element 121 can be arranged in a region between the optical waveguides 117.

The optical waveguide 117, the optical coupler 115, and the modulator 121 are formed using an SOI (Silicon On Insulation) substrate having a silicon oxide film (SiO ₂ film) and a crystalline silicon film formed on the surface thereof. The The silicon oxide film of the SOI substrate becomes the lower cladding layer, and the crystalline silicon film becomes the core layer.

  The case where the present invention is applied to an optical transmitter having a total transmission capacity of 10 Tb / s will be described below. In order to realize a transmission capacity of 10 Tb / s, in this embodiment, 32 edge-emitting DFB lasers capable of continuous oscillation are used as the light emitting element 111. The wavelengths of light emitted from these DFB lasers are assumed to be 50 GHz intervals (about 0.4 nm intervals) centering on 1.55 μm.

  The optical coupler 115 multiplexes light of different wavelengths emitted from these 32 DFB lasers to generate wavelength multiplexed continuous light, and outputs the wavelength multiplexed continuous light to 32 optical waveguides 117. These 32 optical waveguides 117 are connected in series with 32 modulators 121 having different wavelengths of light to be modulated. These modulators 121 are driven at a speed of 10 Gb / s by an electric signal sent from the LSI 114, and each modulates light of a predetermined wavelength. The 32 WDM optical signals modulated by these modulators 121 pass through the 32 optical waveguides 113 a provided in the optical waveguide array 113 and are mounted on the same printed circuit board 110 or other printed circuit boards. Sent to the receiver.

  In such an optical transmitter, the total transmission capacity is 10.24 Tb / s (= 32 (multiplicity of WDM optical signals) × 32 (number of optical waveguides) × 10 Gb / s (modulation speed of the modulator)). . In the optical transmitter according to the present embodiment, the number of light emitting elements 111 required to realize a transmission capacity of 10 Tb / s is as small as 32. Further, the number of optical waveguides 117 in the modulator integrated element 112 is as small as 32, and in combination with the use of a ring-shaped resonant optical modulator that is easy to miniaturize, the optical transmitter can be downsized. Is easy. For example, in the case of an optical transmitter having a total transmission capacity of 10 Tb / s, the size can be equal to or smaller than that of a driving LSI (for example, 1 cm square).

  Furthermore, since the optical transmitter according to the present embodiment can be manufactured relatively easily by using a semiconductor manufacturing technique, there are also advantages that the manufacturing cost is low and the reliability is high. In the present embodiment, since the modulated light is not generated by the light emitting element, the light emitting element 111 that emits light continuously can be used.

  Furthermore, since the optical coupler 115 and the modulator array 116 are integrally formed by the lower clad layer, the core layer, and the upper clad layer on the silicon substrate 130, the optical transmitter of this embodiment should be optically coupled. The portion may be only between the light emitting element 111 and the modulator integrated element 121 and between the modulator integrated element 121 and the optical waveguide array 113, and the assembling work is easy.

  Furthermore, in the optical transmitter according to the present embodiment, the light emitted from the light emitting element 111 is modulated while being moved in a direction parallel to the surface of the printed circuit board 110. Therefore, as shown in FIGS. It is not necessary to secure a space for arranging a mirror or an optical fiber that changes the traveling direction of an optical signal emitted in a direction perpendicular to the substrate surface, and the apparatus can be easily reduced in size.

(Second Embodiment)
FIG. 13 is a perspective view showing an optical transmitter for interconnection according to the second embodiment of the present invention. Note that this embodiment is different from the first embodiment in that the mounting method of the light emitting element 111 is different, and other configurations are basically the same as those of the first embodiment. The same reference numerals are assigned to the same components, and detailed description thereof is omitted.

  In the present embodiment, as shown in FIG. 13, a terrace portion (stepped portion) 112a is provided on the input side (left side in FIG. 13) of the modulator integrated element 112, and the light emitting element 111 is provided on the terrace portion 112a. Is installed. The terrace portion 112a is provided with marks (not shown) for alignment with the light emitting element 111, and the light emitting element 111 and the modulator are arranged by using the marks to place the light emitting element 111 at a predetermined position. The optical waveguide of the integrated element 112 can be optically coupled.

  In the first embodiment described above, since the light emitting element 111 and the modulator integrated element 112 are individually mounted on the printed circuit board 110, it is difficult to align the light emitting element 111 and the modulator integrated element 112, and mass production is possible. May be bad. On the other hand, in the present embodiment, alignment marks are provided in advance on the terrace portion 112a of the modulator integrated element 112, and the light emitting element 111 is mounted at a predetermined position of the modulator integrated element 112 using these alignment marks. Therefore, there is an advantage that the mass productivity is superior to that of the first embodiment.

In the first and second embodiments, the optical waveguide 117, the optical coupler 115, and the modulator 121 are formed by a film made of a silicon material (Si film and SiO ₂ film) formed on a silicon substrate. However, the present invention is not limited to this. For example, the optical waveguide 117, the optical coupler 115, and the modulator 121 may be formed of an InP substrate or a GaAs substrate and a film made of a material that lattice matches with the substrate.

  In the first and second embodiments, the case where the ring-shaped resonant optical modulator having the wavelength selection function having the structure shown in FIG. 10 is used has been described. However, an element having a wavelength selection function and a modulation element are included. It may be formed individually.

  Furthermore, in the first and second embodiments, the case where an edge-emitting DFB laser is used as the light emitting element 111 has been described, but the present invention is not limited to this. For example, a surface emitting laser or a multi-wavelength simultaneous light source may be used as the light emitting element 111.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1) an optical waveguide to which continuous light is input;
A plurality of modulators arranged along the optical waveguide and modulating light passing through the optical waveguide according to an electrical signal supplied from the outside;
An optical signal output unit that outputs light modulated by the plurality of modulators,
The plurality of modulators have different wavelengths of light that can be modulated, respectively.

(Appendix 2) Furthermore, a plurality of light emitting elements that generate continuous light of different wavelengths,
The optical transmitter according to claim 1, further comprising: an optical coupler that multiplexes continuous light emitted from the plurality of light emitting elements and supplies the multiplexed light to the optical waveguide.

  (Additional remark 3) The said optical signal output part outputs the light modulated by these modulators in the direction parallel to the surface of a support substrate, The optical transmitter of Additional remark 1 characterized by the above-mentioned.

(Supplementary Note 4) M optical waveguides (where M is an integer of 2 or more);
A continuous light supply unit for supplying continuous light to each of the M optical waveguides;
A modulator which is connected in series to each of the M optical waveguides (where N is an integer of 2 or more) and modulates the light passing through the optical waveguide according to an electric signal supplied from the outside. When,
An optical signal output unit that outputs light modulated by the N modulators for each of the M optical waveguides;
An optical transmitter characterized in that the N modulators connected in series to one optical waveguide have different wavelengths of light that can be modulated.

  (Additional remark 5) The said continuous light supply part multiplexes the N light emitting elements which generate | occur | produce continuous light of a mutually different wavelength, and the continuous light radiate | emitted from the said N light emitting elements, and said M optical waveguides The optical transmitter according to appendix 4, characterized in that each of the optical transmitters is supplied to the optical coupler.

  (Supplementary note 6) The optical transmitter according to supplementary note 5, wherein each of the light emitting elements is a DFB (Distributed Feed-Back) laser.

  (Supplementary note 7) The optical transmitter according to supplementary note 5, wherein the optical waveguide, the modulator, and the optical coupler are integrally formed.

  (Additional remark 8) The said optical waveguide, the said modulator, and the said optical coupler are comprised by the lower clad layer, core layer, and upper clad layer which were formed on the same semiconductor substrate, The additional mark 5 characterized by the above-mentioned. Optical transmitter.

  (Supplementary note 9) The optical transmitter according to supplementary note 8, wherein the light emitting element is mounted on the semiconductor substrate.

  (Supplementary note 10) The optical transmitter according to supplementary note 5, wherein the optical waveguide, the modulator, and the optical coupler are all formed of silicon or a silicon compound.

  (Supplementary note 11) The optical transmitter according to supplementary note 5, wherein the optical waveguide, the modulator, and the optical coupler are formed using an SOI (Silicon On Insulator) substrate.

  (Supplementary note 12) The optical transmitter according to supplementary note 4, wherein an electrode for connecting to the semiconductor device that supplies the electrical signal is disposed above the modulator.

  (Supplementary note 13) The optical transmitter according to supplementary note 12, wherein the modulator is flip-chip bonded to the semiconductor device.

  (Additional remark 14) The said optical signal output part outputs the light modulated by the said modulator in the direction parallel to the surface of a support substrate, The optical transmitter of Additional remark 4 characterized by the above-mentioned.

  (Supplementary note 15) The optical transmitter according to supplementary note 4, wherein the modulator is a ring resonance type optical modulator.

  (Supplementary note 16) The optical transmitter according to supplementary note 4, wherein the N modulators modulate light having a wavelength of 50 GHz with 1.55 μm as a center.

FIG. 1 is a schematic diagram illustrating a conventional optical transmitter for optical interconnection (part 1). 2A is a schematic diagram showing a conventional optical interconnection optical transmitter (part 2), and FIG. 2B is a diagram showing the arrangement of VCSELs of the optical transmitter. FIG. 3A is a schematic diagram showing a conventional optical interconnection optical transmitter (part 3), and FIG. 3B is a diagram showing the arrangement of VCSELs of the optical transmitter. FIG. 4 is a perspective view showing an optical transmitter for interconnection according to the first embodiment of the present invention. FIG. 5 is a block diagram illustrating a configuration of the optical transmitter according to the first embodiment. FIG. 6 is a schematic diagram showing the concept of the operation of the modulator. FIG. 7A is a cross-sectional view showing the structure of the optical waveguide of the modulator integrated device, and FIG. 7B is a diagram for explaining the size of each part of the optical waveguide. FIG. 8A is a top view showing the configuration of the optical coupler, and FIG. 8B is a diagram for explaining the size of each part of the optical coupler. FIG. 9 is an enlarged view of a portion surrounded by a broken line A in FIG. FIG. 10 is a top view showing the configuration of the modulator. FIG. 11 is a cross-sectional view of the ring-shaped optical waveguide of the modulator. 12A and 12B are diagrams showing the characteristics of the modulator, FIG. 13 is a perspective view showing an optical transmitter for interconnection according to the second embodiment of the present invention.

Explanation of symbols

10, 20, 30, 110 ... printed circuit board,
11, 21, 31, 114 ... LSI,
12, 22, 32 ... VCSEL,
13, 113 ... Optical waveguide array,
23, 34a ... micro lens array,
24 ... 45 degree mirror,
34: Optical multiplexer,
34b ... micro lens,
35 ... Optical fiber,
111 ... light emitting element,
112 ... modulation integrated element,
112a ... terrace,
115 ... optical coupler,
116 ... modulator array section,
117, 141a, 141b, 143a, 143b ... optical waveguide,
121. Modulator,
130 ... silicon substrate,
131, 133 ... SiO ₂ layer,
132 ... Si layer,
132a ... core,
132b ... Si thin film,
141: Input port side optical waveguide array,
142 ... slab waveguide section,
143 ... Output port side optical waveguide array,
151a, 151b, 151c ... ring-shaped optical waveguide,
152 ... Drop port.

Claims (9)

An optical waveguide to which continuous light is input;
A plurality of modulators arranged along the optical waveguide and modulating light passing through the optical waveguide according to an electrical signal supplied from the outside;
An optical signal output unit that outputs light modulated by the plurality of modulators,
The plurality of modulators have different wavelengths of light that can be modulated, respectively. M optical waveguides (where M is an integer of 2 or more);
A continuous light supply unit for supplying continuous light to each of the M optical waveguides;
A modulator which is connected in series to each of the M optical waveguides (where N is an integer of 2 or more) and modulates the light passing through the optical waveguide according to an electric signal supplied from the outside. When,
An optical signal output unit that outputs light modulated by the N modulators for each of the M optical waveguides;
An optical transmitter characterized in that the N modulators connected in series to one optical waveguide have different wavelengths of light that can be modulated.   The continuous light supply unit multiplexes the N light emitting elements that generate continuous light having different wavelengths and the continuous light emitted from the N light emitting elements, and supplies the multiplexed light to the M optical waveguides. The optical transmitter according to claim 2, comprising an optical coupler.   The optical transmitter according to claim 3, wherein each of the light emitting elements is a DFB (Distributed Feed-Back) laser.   4. The optical transmitter according to claim 3, wherein the optical waveguide, the modulator, and the optical coupler are configured by a lower clad layer, a core layer, and an upper clad layer formed on the same semiconductor substrate. .   The optical transmitter according to claim 5, wherein the light emitting element is mounted on the semiconductor substrate.   The optical transmitter according to claim 2, wherein an electrode for connecting to the semiconductor device that supplies the electrical signal is disposed above the modulator.   The optical transmitter according to claim 7, wherein the modulator is flip-chip bonded to the semiconductor device.   The optical transmitter according to claim 2, wherein the optical signal output unit outputs the light modulated by the modulator in a direction parallel to the surface of the support substrate.

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