JP2017098362A - Optical integrated device and optical communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical integrated device in which the number of elements and the number of mounting times are reduced, which is easily mounted, and in which a low cost is realized.SOLUTION: An optical integrated device 3 comprises: a first semiconductor optical amplifier 4 and a second semiconductor optical amplifier 5. Both end surfaces 6 which a light enters, comprises: an optical semiconductor element 1 to be anti-reflection coated; a waveguide type mirror 7; a partial reflection mirror 8 of the waveguide type; an optical waveguide path 9 provided between the partial reflection mirror 8 and the mirror 7; a wavelength filter 10 of the waveguide type which is provided to the optical waveguide path 9 and includes ring resonators 10A and 10B; and an optical function element 2 comprising an outside optical waveguide path 12 provided between the partial reflection mirror 8 and an output end surface 11. The optical semiconductor element and the optical function element are accumulated so that the first semiconductor optical amplifier 4 is optically connected to the optical waveguide path 9, and the second semiconductor optical amplifier 5 is optically connected to the outside optical waveguide path.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical integrated device and an optical communication device.

As an optical integrated element, for example, there is a wavelength tunable laser in which three elements of a silicon waveguide tunable filter including a ring resonator, a gain chip, and a booster SOA (semiconductor optical amplifier) are integrated on a silicon platform.
In this wavelength tunable laser, a ring resonator is provided inside a laser resonator formed between a reflecting mirror provided in a silicon waveguide tunable filter and a reflecting film provided on an end face of a gain chip. Become.

  When a laser is configured by integrating SOA (gain chip) as a gain medium, a laser resonator is generally configured using a reflection film provided on the end face of the SOA.

JP 2010-087472 A JP 2007-248901 A JP 2006-245346 A

K. Sato et al., “High Output Power and Narrow Linewidth Silicon Photonic Hybrid Ring-Filter External Cavity Wavelength Tunable Lasers”, European Conference on Optical Communication (ECOC), lecture number PD.2.3, 2014

  By the way, when the ring resonator is provided inside the laser resonator as in the above-described wavelength tunable laser, the light intensity inside the laser resonator is sufficiently high in order to suppress the complicated behavior of the ring resonator due to the optical nonlinear effect. The laser operation is performed while suppressing the magnitude of the current injected into the gain chip to be small. For this reason, the power of the laser beam output from the end face of the gain chip is reduced. Therefore, like the above-described wavelength tunable laser, a booster SOA is further integrated on the output side of the gain chip, and a large output can be obtained by amplifying the laser light output from the gain chip. .

However, in this case, three elements are integrated, and the number of elements to be mounted increases.
Such an increase in the number of necessary elements causes an increase in cost, which is not preferable.
Moreover, when mounting these elements, in order to suppress the optical coupling loss between the elements, a precise alignment accuracy of less than a micron is required between the elements.

For this reason, when the number of elements to be mounted increases, the number of such highly difficult mounting increases, resulting in an increase in manufacturing cost.
In one aspect, it is an object to reduce the number of elements and the number of times of mounting to facilitate mounting and reduce costs.

  In one aspect, an optical integrated device includes a first semiconductor optical amplifier and a second semiconductor optical amplifier, an optical semiconductor device in which both end faces to which light is input and output are coated with antireflection, a waveguide type mirror, A waveguide type partial reflection mirror, an optical waveguide provided between the partial reflection mirror and the mirror, a waveguide type wavelength filter provided in the optical waveguide and including a ring resonator, a partial reflection mirror and an output And an optical functional element including an output-side optical waveguide provided between the first and second end faces, the first semiconductor optical amplifier is optically connected to the optical waveguide, and the second semiconductor optical amplifier is connected to the output-side optical waveguide. An optical semiconductor element and an optical functional element are integrated so as to be optically connected to the waveguide.

  In one aspect, an optical communication apparatus includes the above-described optical integrated device.

  As one aspect, there is an effect that the number of elements and the number of mountings can be reduced, the mounting can be facilitated, and the cost can be reduced.

(A), (B) is a schematic diagram which shows the structure of the optical integrated device concerning this embodiment, (A) is a top view, (B) is sectional drawing. It is a typical sectional view showing the composition of the optical semiconductor device which constitutes the optical integrated device concerning this embodiment. It is a typical sectional view showing composition of an optical functional element which constitutes an optical integrated element concerning this embodiment. It is a typical top view which shows the structure of the optical integrated element concerning the 1st modification of this embodiment. It is a typical top view which shows the structure of the optical integrated element concerning the 2nd modification of this embodiment. It is a typical top view showing composition of an optical integrated device concerning the 3rd modification of this embodiment. It is a schematic plan view which shows the structure of the optical integrated element concerning the 4th modification of this embodiment. (A), (B) is typical sectional drawing which shows the structure of the optical semiconductor element which comprises the optical integrated element concerning the 4th modification of this embodiment, (A) is a cross section in the direction along an optical axis. FIG. 4B is a cross-sectional view taken along a direction perpendicular to the optical axis of the DBR portion. It is a typical top view showing composition of an optical integrated device concerning the 5th modification of this embodiment. It is a schematic plan view which shows the structure of the optical integrated element concerning the 6th modification of this embodiment.

Hereinafter, an optical integrated device and an optical communication apparatus according to embodiments of the present invention will be described with reference to FIGS.
The optical integrated device according to the present embodiment is, for example, a laser device for communication, and is provided in an optical communication device such as an optical transmitter, an optical receiver, or an optical transceiver, and is used in, for example, an optical transmission device.

As shown in FIG. 1, the optical integrated device of this embodiment is an optical integrated device 3 in which an optical semiconductor device 1 and an optical functional device 2 made of different materials are integrated. Note that the optical semiconductor element and the optical functional element are also simply referred to as optical elements.
Here, the optical semiconductor device 1 includes a first SOA (first semiconductor optical amplifier) 4 and a second SOA (second semiconductor optical amplifier) 5, and both end faces 6 through which light is input and output are coated with no reflection (AR). ing. Here, the optical semiconductor element 1 is formed on an InP substrate, and the first SOA 4 and the second SOA 5 are arranged in an array. For this reason, the optical semiconductor element 1 is also referred to as an InP-SOA array element or an SOA array element. Here, the optical semiconductor element 1 is made of an InP-based material formed on an InP substrate, but is not limited to this, and is made of, for example, a GaAs-based material formed on a GaAs substrate. There may be.

  The optical functional element 2 includes a waveguide type mirror 7, a waveguide type partial reflection mirror 8, and an optical waveguide (laser side optical waveguide) 9 provided between the partial reflection mirror 8 and the mirror 7. A waveguide-type wavelength filter 10 provided in the optical waveguide 9 and including a ring resonator, and an output-side optical waveguide 12 provided between the partial reflection mirror 8 and the output end face 11. Here, the optical functional element 2 also includes a phase adjuster 13 provided in the optical waveguide 9. For example, the phase adjuster 13 is a phase adjuster composed of a Si waveguide with a heater 13X. The optical functional element 2 may be configured not to include the phase adjuster 13. In FIG. 1A, reference numeral 10X denotes a heater. In FIGS. 1A and 1B, reference numeral 202 denotes a waveguide core (here, Si waveguide core). 1A and 1B, reference numeral 102 denotes a waveguide core (in this case, an SOA waveguide core). In FIGS. 1A and 1B, reference numeral 14 denotes a recess (terrace).

  Here, the optical functional element 2 is made of a Si-based material formed on the Si substrate 200, and includes a mirror 7, a partial reflection mirror 8, an optical waveguide 9, a wavelength filter 10, an output-side optical waveguide 12, and phase adjustment. The vessel 13 is constituted by a Si waveguide (Si waveguide core 202). That is, here, the optical functional element 2 is a silicon waveguide substrate (Si waveguide substrate). Further, here, the mirror 7 and one input / output end (port) of the partial reflection mirror 8 are optically connected (optically coupled) by the optical waveguide 9, and the optical waveguide 9 is connected to the optical waveguide 9 from the mirror 7 side. In order, a wavelength filter 10 and a phase adjuster 13 are provided, and the other input / output end (port) of the partial reflection mirror 8 and the output end face 11 are optically connected by an output side optical waveguide 12 (optical coupling). ) Since these are optical circuits constituted by Si waveguides, they are also called optical circuits on the Si substrate. The optical functional element 2 is also referred to as an optical circuit element, an optical circuit element on a Si substrate, or an optical waveguide substrate.

The mirror 7 is a loop mirror. Here, the mirror 7 is a loop mirror, but is not limited thereto, and may be another waveguide type mirror such as a diffraction grating mirror (for example, a DBR mirror).
The wavelength filter 10 is a ring resonator type wavelength filter including a ring resonator. Here, the wavelength filter 10 is a vernier type wavelength filter using two ring resonators 10A and 10B. Specifically, the wavelength filter 10 is a vernier type tunable filter in which two ring resonators 10A and 10B provided with a heater (heater electrode) 10X for controlling the refractive index of the waveguide are connected. . The optical integrated element 3 is also referred to as a wavelength tunable laser element or a wavelength tunable laser light source.

  The optical semiconductor element 1 and the optical functional element 2 are hybrid-integrated so that the first SOA 4 is optically connected to the optical waveguide 9 and the second SOA 5 is optically connected to the output-side optical waveguide 12. ing. Here, a recess (terrace) 14 is provided on the surface of a silicon waveguide substrate as the optical functional element 2 by, for example, etching, and the InP-SOA array element 1 is flip-chip mounted in the recess 14. Yes. The end portions of the waveguides are exposed at the end surface of the InP-SOA array element 1 and the side surfaces of the recesses 14 provided in the silicon waveguide substrate 2, and these waveguides are formed by flip chip mounting. They are optically coupled to each other.

  Here, an optical waveguide 9 provided between the mirror 7 and the partial reflection mirror 8 is provided with a wavelength filter 10 including a ring resonator, and the first SOA 4 is optically connected to the optical waveguide 9. It is connected. That is, the optical input / output units at both ends of the first SOA 4 are optically coupled to the mirror 7 and the partial reflection mirror 8, respectively. Here, one of the light input / output units at both ends of the first SOA 4 is optically coupled to the partial reflection mirror 8, and the other is optically coupled to the mirror 7 via the wavelength filter 10. In the present embodiment, a recess 14 is provided on the surface of a silicon waveguide substrate as the optical functional element 2 so as to divide the optical waveguide 9 into two parts. The wavelength filter 10 and the mirror 7 are provided on one side of the optical waveguide 9 with the concave portion 14 in between, and the partial reflection mirror 8 is provided on the other side portion. Since the SOA array element 1 is mounted, these portions and the first SOA 4 are optically coupled.

As described above, the first SOA (SOA having optical gain) 4 as a gain medium is provided between the mirror 7 and the partial reflection mirror 8 to constitute a laser resonator, and a current is passed through the first SOA 4. The generation and amplification of light are performed, and laser operation can be obtained.
A wavelength filter 10 including a ring resonator is provided inside the laser resonator. Here, a vernier type wavelength tunable filter 10 including two ring resonators 10A and 10B with a heater is provided between the mirror 7 and the first SOA 4. The tunable filter 10 has a function of selectively transmitting only a single wavelength by the two ring resonators 10A and 10B and controlling the wavelength by the heater 10X. As a result, laser operation is performed at a single controlled wavelength, and wavelength variable operation can be obtained.

Further, a phase adjuster 13 composed of a Si waveguide with a heater 13X is provided between the first SOA 4 and the partial reflection mirror 8, and the optical path length of the laser resonator can be finely adjusted by the phase adjuster 13. Thus, laser operation in a single resonator mode can be stably obtained.
A second SOA 5 as a booster is optically connected to an output-side optical waveguide 12 provided between the partial reflection mirror 8 and the output end face 11. That is, the partial reflection mirror 8 outputs a part of the light input from the first SOA 4 to the second SOA 5 via the output side optical waveguide 12. In the present embodiment, a recess 14 is provided on the surface of a silicon waveguide substrate as the optical functional element 2 so as to divide the output-side optical waveguide 12 into two parts. The end surface of one side of the output-side optical waveguide 12 with the concave portion 14 interposed therebetween, that is, the end surface of the Si waveguide substrate as the optical functional element 2 is the output end surface, and is partially formed on the other side. A reflection mirror 8 is provided, and the InP-SOA array element 1 is mounted in the recess 14 so that these portions and the second SOA 5 are optically coupled.

  As described above, the laser light traveling back and forth in the waveguide in the laser resonator is output from the partial reflection mirror 8 provided at one end of the laser resonator with a part of the optical power connected to the outside of the laser resonator. It is output to the optical waveguide (Si waveguide) 12. The laser light is amplified by the second SOA 5 optically connected to the output-side optical waveguide 12 and then output from the output end face 11.

As described above, the laser resonator is configured by disposing the first SOA 4 and the wavelength filter 10 between the mirror 7 and the partial reflection mirror 8, and the laser light is amplified by the second SOA 5 outside the laser resonator. The wavelength tunable laser is configured. For this reason, a compact wavelength tunable laser with a large optical output can be obtained.
Further, as described above, the wavelength filter 10 is a vernier type tunable filter. Further, the silicon waveguide has a large light confinement, and the bending radius of the waveguide can be reduced to about 10 μm or less. For this reason, the optical circuit required for the wavelength tunable laser can be configured in a compact manner, and the wavelength tunable laser can be reduced in size.

  Further, as described above, since the ring resonator is provided inside the laser resonator, in order to suppress the complicated behavior of the ring resonator due to the optical nonlinear effect, the light intensity inside the laser resonator is sufficiently reduced. The laser operation is performed while suppressing the magnitude of the current injected into the first SOA 4. For this reason, the power of the laser beam output from the partial reflection mirror 8 to the output end face 11 is reduced. Therefore, a second SOA 5 as a booster is provided between the partial reflection mirror 8 and the output end face 11, and a large output can be obtained by amplifying the laser light output from the partial reflection mirror 8 to the output end face 11 side. I am doing so.

In particular, here, the first SOA 4 and the second SOA 5 are provided in a single optical semiconductor element 1, the optical semiconductor element 1 and the optical functional element 2 are integrated, and only the two elements 1 and 2 are integrated. By reducing the number of elements and the number of mountings, mounting can be facilitated and cost reduction can be realized.
Here, the first SOA 4 as a gain medium and the second SOA 5 as a booster are provided in a single optical semiconductor element 1. A non-reflective coating is applied to both end faces 6 of the optical semiconductor element 1, and a laser resonator is configured using a waveguide type mirror 7 and a waveguide type partial reflection mirror 8.

For example, two SOAs may be integrated by sandwiching a diffraction grating mirror (DBR mirror) between two SOAs. However, when a diffraction grating mirror is provided in an InP-based optical semiconductor element, a laser resonator is used. It is difficult to obtain a constant reflectivity (for example, about 30%) comparable to that of the constituting end face mirror in the operating wavelength band of the wavelength tunable laser.
As described above, the Si light including the optical filter 1 formed on the InP substrate and including the first SOA 4 as the gain medium and the second SOA 5 as the booster, and the wavelength filter 10 formed on the Si substrate and including the Si waveguide. A tunable laser is constituted by an optical integrated element 3 in which an optical functional element 2 having a circuit is integrated, thereby enabling a high-power operation and a simple element with a reduced number of required elements in a compact and narrow linewidth tunable laser. Depending on the configuration, it can be realized at low cost.

Next, the structure of each element constituting the wavelength tunable laser will be described with a specific example.
First, the structure of the InP-SOA array element as the optical semiconductor element 1 will be described.
Here, FIG. 2 is a cross-sectional view showing a cross-sectional structure of a portion including the waveguide core layer of the first SOA 4 of the InP-SOA array element, that is, a cross-sectional view taken along the line AA in FIG. .
Here, the first SOA 4 and the second SOA 5 included in the InP-SOA array element 1 have the same structure.

As shown in FIG. 2, the InP-SOA array element 1 is formed on an n-type InP substrate 101, and an InGaAsP-based multiquantum well (MQW; MQW) having a gain in a 1.55 μm band is provided in a portion of the first SOA 4. An optical waveguide (SOA waveguide) including a core layer (waveguide core layer) 102 made of a multiple quantum well active layer and a clad layer 103 made of a p-InP layer formed thereon is formed. A p-InGaAsP / InGaAs contact layer 104 is formed on the p-InP layer as the cladding layer 103. The core layer 102, the clad layer 103, and the contact layer 104 are striped, and both sides thereof are embedded with a semi-insulating InP layer (SI-InP layer) 105. A p-side electrode 106 and an n-side electrode 107 for flowing current are formed on both the upper and lower surfaces of the SOA waveguide. The p-side electrode 106 is in contact with the semiconductor only above the SOA waveguide, and the other part is covered with the SiO ₂ passivation film 108.

  As shown in FIG. 1B, the InP-SOA array element 1 configured as described above is turned upside down so that the n-type InP substrate 101 is on the upper side. The chip is flip-chip mounted on a recess (terrace) 14 formed so as to be continuous with the Si waveguide (Si waveguide core 202) on the Si substrate 200 provided in the waveguide substrate. By mounting in this way, the height of the waveguide core layer 102 of the InP-SOA array element 1 is precisely determined by the thicknesses of the p-InP cladding layer 103, the p-InGaAsP / InGaAs contact layer 104, and the p-side electrode 106. Therefore, the height alignment with the Si waveguide core 202 is facilitated.

  Further, the InP-SOA array element 1 preferably has a length of, for example, 600 μm, and the waveguide is inclined by about 7 ° with respect to the end face in the vicinity of the end face (see, for example, FIG. 1A). Thereby, unnecessary reflection at the end faces of the first SOA 4 and the second SOA 5 can be suppressed, and the operation of the laser can be stabilized. In addition, antireflection (AR) coating is applied to both end faces 6 of the InP-SOA array element 1 where the end portions of the waveguides are exposed to prevent reflection.

Next, the structure of the Si waveguide substrate as the optical functional element 2 will be described.
First, the mirror 7, the partial reflection mirror 8, the optical waveguide 9, the wavelength filter 10, the output-side optical waveguide 12, and the phase adjuster 13 provided in the Si waveguide substrate 2 are arranged in the Si waveguide ( It is constituted by a Si waveguide core 202).
Here, the Si waveguide provided in the Si waveguide substrate 2 is formed using an SOI (Silicon On Insulator) substrate and formed on the Si substrate 200 with a width of about 0.5 μm and a thickness of about 0.2 μm, for example. It has a waveguide structure in which the upper and lower sides of the Si core layer 202 covered are covered with SiO ₂ cladding layers 201 and 203 (see FIG. 3).

Here, FIG. 3 is a cross-sectional view showing a cross-sectional structure of a portion of the wavelength filter 10 provided in the Si waveguide substrate 2, that is, a cross-sectional view taken along the line BB in FIG.
As shown in FIG. 3, the wavelength filter 10 provided in the Si waveguide substrate 2 includes two ring waveguides (Si waveguide ring resonator; ring) configured by the Si waveguide 204 provided in the Si waveguide substrate 2. Resonator) and a straight waveguide. In the two ring resonators 10A and 10B, only light having a wavelength that matches the resonance wavelength passes through the ring waveguide, propagates from the drop port to the straight waveguide, and light having other wavelengths passes through the ring waveguide. It propagates from the through port to the straight waveguide without passing through. Here, the heater electrodes 10X are provided on the ring waveguide 204 in the two ring resonators 10A and 10B, and the refractive index is changed by adjusting the temperature of the waveguides of the ring resonators 10A and 10B. Thus, the position of the resonance wavelength can be adjusted. In addition, here, the ring resonators (ring waveguides) are set to have circumferential lengths so that the two ring resonators 10A and 10B have slightly different periods of their resonance wavelengths. For example, the resonance wavelength interval of one ring resonator may be about 6 nm, and the resonance wavelength interval of the other ring resonator may be about 6.82 nm. In order to obtain stable laser operation at a single wavelength, the finesse of the two ring resonators 10A and 10B is preferably set to 8 or more.

Also, the phase adjuster 13 has a structure in which the heater electrode 13X is provided on the Si waveguide 204, similarly to the wavelength filter 10 described above.
The loop mirror 7 is also configured by the Si waveguide 204, and is configured by joining (connecting) the waveguides branched 1: 1 by a 1 × 2 coupler.
The partial reflection mirror 8 is also composed of the Si waveguide 204, and is connected to the other side of the directional coupler in which the laser side optical waveguide 9 and the output side optical waveguide 12 are connected to one side. It is configured by joining (connecting) two waveguides. In this case, the light input from the laser-side optical waveguide 9 is distributed by the directional coupler to two waveguides connected to the other side at an appropriate branching ratio, and a part of the input light power is laser-side optical. Returning to the waveguide 9, the remaining optical power is output to the output-side optical waveguide 12.

  The wavelength tunable laser as the optical integrated device configured as described above is operated in a single mode by the functions of the two SOAs 4 and 5, the vernier tunable filter 10, the phase adjuster 13, the loop mirror 7, and the partial reflection mirror 8. Tunable laser operation can be obtained with a large light output. In particular, by using only two optical elements, that is, a single SOA array element 1 and a Si waveguide substrate 2, it can be manufactured simply and at low cost by only one mounting.

Therefore, according to the optical integrated device and the optical communication device according to the present embodiment, there is an advantage that the number of devices and the number of mountings can be reduced, mounting can be facilitated, and cost can be reduced.
In the above-described embodiment, the end face of the Si waveguide substrate as the optical functional element 2 is used as the output end face 11. However, the present invention is not limited to this.

For example, as shown in FIG. 4, the end face 6 of the optical semiconductor element 1 may be an output end face 11X. This is referred to as a first modification.
In this case, the output from the region where the output end face 11 side portion of the output side optical waveguide 12 of the Si waveguide substrate 2 of the above-described embodiment is formed, that is, from a part of the terrace 14 where the output end of the second SOA 5 is located. By removing the region up to the end surface 11 by, for example, etching or dicing, the end surface 6 of the optical semiconductor element 1 can be used as the output end surface 11X. In this case, the output side optical waveguide 12 is constituted only by the part on the partial reflection mirror 8 side.

  As a result, the laser beam propagating through the second SOA 5 and amplified to a large output is directly output to the outside of the wavelength tunable laser without being coupled to the Si waveguide again as in the above-described embodiment. become. Therefore, the number of optical coupling points between the SOAs 4 and 5 and the Si waveguides 9 and 12 is reduced by one compared with that of the above-described embodiment. As a result, the optical coupling loss can be reduced, and an optical output larger than that of the above-described embodiment can be obtained with a constant operating current.

In the above embodiment, the wavelength filter 10 is a vernier type wavelength filter using two ring resonators 10A and 10B, and the mirror 7 constituting the laser resonator is a loop mirror or a diffraction grating mirror. However, it is not limited to this.
For example, as shown in FIG. 5, the wavelength filter 10 is composed of one ring resonator 10C and a diffraction grating mirror 10D, and this diffraction grating mirror 10D is used as a mirror 7 constituting a laser resonator. Also good. That is, the wavelength filter 10 may be composed of one ring resonator 10C and the diffraction grating mirror 10D, and the mirror 7 may be the diffraction grating mirror 10D. This is referred to as a second modification.

For example, the wavelength filter 10 may be a wavelength tunable filter including a single ring resonator 10C with a heater 10X and a diffraction grating mirror 10D (for example, a DBR mirror).
In the wavelength tunable filter 10 configured as described above, the vernier effect cannot be obtained, so the wavelength tunable width is smaller than that of the above-described embodiment, but on the other hand, since the configuration is simple, There is an advantage that wavelength variable operation can be obtained by simple control.

  Further, in the wavelength tunable filter 10 configured as described above, the ring resonator 10C has a plurality of resonance wavelengths arranged periodically, and transmits propagating light at the plurality of wavelengths. On the other hand, a mirror (DBR) 10D composed of a diffraction grating connected to the subsequent stage of the ring resonator 10C selects light of one or a plurality of wavelengths from among the plurality of wavelengths and selectively reflects it. It has the function to do.

When designing the reflection band of the DBR 10D to be narrow, a single wavelength operation in which only one wavelength is selected is obtained. When designing the reflection band of the DBR 10D to be wide, a plurality of rings included in the DBR reflection band are obtained. Multi-wavelength simultaneous laser operation at the resonant wavelength is obtained. There is also an advantage that such multi-wavelength laser operation can be easily obtained.
Here, in order to obtain a multi-wavelength laser operation, it is preferable that the core layer of the first SOA 4 is suitable for this. For example, a quantum dot active layer formed on a GaAs substrate is used as the core layer of the first SOA 4. Is preferred. This is because quantum dots have a wide wavelength band, and each quantum dot independently contributes to laser operation, so that laser oscillation easily occurs at a plurality of wavelengths.

  A diffraction grating mirror (DBR) 10D made of a Si waveguide can be obtained by, for example, periodically making the width of the Si core layer 202 thicker than, for example, about 0.5 μm in the cross-sectional structure of FIG. Here, the period may be set to a period of about 300 nm for a central operating wavelength of about 1550 nm, for example, so that the Bragg wavelength of the diffraction grating matches the center of the operating wavelength band.

Further, the optical integrated element (see FIG. 5) of the second modified example described above is further provided in the output-side optical waveguide 12 as shown in FIG. 6, and is located between the partial reflection mirror 8 and the second SOA 5. An optical modulator 15 may be provided. This is called a third modification. In FIG. 6, reference numeral 15X denotes an electrode.
In this case, the reflection band of the DBR 10D is set to be relatively narrow so as to select one resonance wavelength of the ring resonator 10C, so that laser operation at a single wavelength is obtained, and the Si waveguide substrate as the optical functional element 2 For example, a Mach-Zehnder type optical modulator (silicon modulator) 15 may be provided in a portion of the output side optical waveguide 12 provided in the side of the partial reflection mirror 8.

By the operation of the modulator 15, the signal light whose light intensity is modulated by the electric signal input to the modulator 15 is output from the wavelength tunable laser element 3 of the third modification.
In the third modification, since the second SOA 5 is provided in the subsequent stage of the modulator 15 as in the second modification described above, high-output signal light can be obtained.
In the third modification, an operation in which the optical loss of the silicon modulator 15 is compensated in advance by the second SOA 5 can be obtained. In other words, since it is sufficient to increase the optical output that has been reduced due to the optical loss by the silicon modulator 15 using the second SOA 5, it is not necessary to anticipate the optical loss in the subsequent stage of the second SOA 5, and the SOA with a low saturated optical output. Can be used as the second SOA 5. Therefore, the power consumption can be reduced in order to obtain the required signal light intensity.

  On the other hand, in the above-described second modified example, a modulator with optical loss is connected to the subsequent stage of the wavelength tunable laser 3, so that the optical output from the second SOA 5 is preliminarily set in consideration thereof. I will take a minute. In this case, an SOA having a high saturation light output is used as the second SOA 5, and the load on the second SOA 5 is increased, and the injection current to the second SOA 5 is increased, which is not desirable from the viewpoint of reducing power consumption.

In the above-described embodiment, the mirror 7 is provided in the optical functional element 2. However, the present invention is not limited to this. For example, the mirror 7 may be provided in the optical semiconductor element 1.
In this case, for example, as shown in FIG. 7, the mirror 7 is a diffraction grating mirror (waveguide type mirror) provided in the optical semiconductor element 1, and the wavelength filter 10 including the ring resonator is partially reflected from the first SOA 4. It is preferable to be positioned between the mirror 8. The wavelength filter 10 including a ring resonator is preferably a vernier type wavelength filter using two ring resonators 10A and 10B. The end face 6 of the optical semiconductor element 1 is preferably the output end face 11. This is called a fourth modification.

  Here, a vernier type wavelength filter 10 provided in the optical functional element 2 and provided in the optical functional element 2 and in the optical waveguide 9 connected to the partial reflection mirror 8 and using the two ring resonators 10A and 10B is provided. Furthermore, the first SOA 4 provided in the optical semiconductor element 1 is optically connected to the optical waveguide 9. That is, one of the light input / output units at both ends of the first SOA 4 provided in the optical semiconductor element 1 is connected to the partial reflection mirror 8 provided in the optical functional element 2 via the wavelength filter 10 provided in the optical functional element 2. The other is optically coupled to a mirror 7 provided in the optical semiconductor element 1.

Specifically, the InP-SOA array element 1 on the InP substrate is configured such that the first SOA 4 and the second SOA 5 are arranged in an array, and further, an end face on one side of the second SOA 5, that is, the optical semiconductor element 1. The end face of the InP-SOA array element is an output end face 11, and a diffraction grating mirror as a mirror 7 is provided on the output end face 11 side of the first SOA 4.
Further, an optical circuit element (Si waveguide substrate) 2 on a Si substrate is made up of an optical waveguide 9, a wavelength filter 10, a phase adjuster 13, a partial reflection mirror 8, an output side optical waveguide 12, which are configured by Si waveguides. Further, a concave portion (terrace) 14 extending to the end surface of the Si substrate, that is, a concave portion 14 having no side wall on the end surface side of the Si substrate is provided, and one end portion of the optical waveguide 9 and the output side optical waveguide 12 is provided in the concave portion 14. And one input / output end of the partial reflection mirror 8 is connected to the other end of the optical waveguide 9 via the wavelength filter 10 and the phase adjuster 13, and the other end of the output-side optical waveguide 12 is connected. Is connected to the other input / output end of the partial reflection mirror 8.

  Then, by mounting the InP-SOA array element 1 in the recess 14 of the optical circuit element 2 on the Si substrate, an optical waveguide is formed on the side opposite to the end face 6 side that becomes the output end face 11 of the InP-SOA array element 1. 9 and the first SOA 4 are optically coupled, the output-side optical waveguide 12 and the second SOA 5 are optically coupled, and the end surface 6 serving as the output end surface 11 of the InP-SOA array element 1 is exposed to the outside. Yes.

  In this case, an optical waveguide 9 is provided between the mirror 7 and the partial reflection mirror 8, a wavelength filter 10 is provided on the optical waveguide 9, and the first SOA 4 is optically connected to the optical waveguide 9. become. Further, an output-side optical waveguide 12 is provided between the partial reflection mirror 8 and the output end face 11, and the second SOA 5 is optically connected to the output-side optical waveguide 12. Further, a diffraction grating mirror as a mirror 7 provided on the output end face 11 side of the first SOA 4 and integrated on the InP substrate on which the first SOA 4 is provided, and a portion provided on the optical circuit element 2 on the Si substrate. A laser resonator in which the first SOA 4 and the wavelength filter 10 are disposed between the reflection mirror 8 and the reflection mirror 8 is configured. Note that both end faces 6 of the InP-SOA array element 1 are coated with antireflection as in the case of the above-described embodiment, but a diffraction grating mirror 7 is provided on the output end face 11 side of the first SOA 4. Therefore, the propagating light is reflected by the diffraction grating mirror 7 in front of the end face. In addition, the light input to the second SOA 5 from the output-side optical waveguide 12 of the optical circuit element 2 on the Si substrate is amplified by the second SOA 5 and again without being optically coupled to the optical circuit element 2 on the Si substrate. , And output from the opposite side of the second SOA 5 to the outside.

  By adopting such a configuration, the InP-SOA array element 1 is optically coupled to the optical circuit element 2 on the Si substrate only on one end face. This facilitates optical coupling by flip chip mounting. In addition, the number of optical couplings between the waveguides straddling the two elements 1 and 2 in the entire tunable laser is reduced to two places as compared with the four places in the above-described embodiment. Thereby, the optical coupling loss can be reduced, and the power consumption required to obtain a constant light output is reduced.

Here, FIG. 8 shows the structure of a DBR (Distributed Bragg Reflector) which is a diffraction grating mirror integrated in an InP-SOA array element.
Here, as shown in FIG. 8A, the DBR portion 7X, which is a portion where the diffraction grating mirror 7 of the InP-SOA array element 1 is provided, is divided into, for example, 20 blocks. The period of the diffraction grating 109 is changed so that the Bragg wavelength of the diffraction grating 109 sequentially changes, for example, from about 1525 nm to about 1565 nm in steps of about 2 nm from the side closer to the SOA part 4X where the first SOA 4 is provided. Is changing. Thereby, it is possible to form a DBR (DBR mirror 7) having a flat reflectance in a C-band band (about 1525 to about 1565 nm) often used as a used wavelength band in optical communication. Here, the length of each block of the DBR portion 7X may be about 50 μm, for example, and the total length may be about 1000 μm. Further, the reflectance of the DBR portion 7X may be set to a reflectance close to 100% by appropriately adjusting the coupling coefficient of the diffraction grating 109. It should be noted that obtaining a flat reflection spectrum with a reflectance close to 100% can be realized relatively easily by sufficiently increasing the length of the DBR while changing the DBR period.

Here, as shown in FIG. 8B, the DBR portion 7X is formed on the n-InP substrate 101, for example, an InGaAsP core layer (waveguide core layer) 110 having a composition of about 1.3 μm, and a p-InP cladding layer 103. Are stacked, and a diffraction grating 109 is formed in the vicinity (here, the lower side) of the core layer 110. In the DBR portion 7X, as in the SOA portion 4X, the core layer 110, the clad layer 103, a part of the substrate 101, etc. are removed by etching except the portion that becomes the waveguide, and the side thereof is semi-insulating. (SI) The InP layer 105 is embedded. The surface is covered with a SiO ₂ passivation film 108. In the DBR portion 7X, since it is not necessary to pass a current through the core layer 110, the p-InGaAsP / InGaAs contact layer 104 and the p-side electrode 106 (FIG. 2) provided above the core layer 110 are provided in the SOA portion 4X. Reference) is not provided.

Moreover, although the above-mentioned embodiment and the 1st modification-a 4th modification are each demonstrated separately, it is also possible to combine these arbitrarily. For example, the first modified example can be applied to the second modified example and the third modified example. Further, for example, the third modification can be applied to the embodiment and the first modification.
Further, in the above-described embodiment and each modified example, two SOAs are provided in an InP-SOA array element as an optical semiconductor element, but the present invention is not limited to this, and it is assumed that three or more SOAs are provided. Also good.

  For example, in the above-described embodiment and each modified example, one SOA is added to the InP-SOA array element as the optical semiconductor element 1, and this added SOA is added to the optical circuit element on the Si substrate as the optical functional element 2. By providing a Si waveguide that is optically coupled to the laser beam, the laser beam amplified by the second SOA may be further amplified by the added SOA.

  For example, as shown in FIG. 9, the optical functional element 2 of the third modified example (see FIG. 6) is assumed to be connected to the silicon modulator 15 in parallel with another silicon modulator 16. The two silicon modulators (Mach-Zehnder modulators) 15 and 16 constitute an IQ modulator (orthogonal modulator; optical modulator) 17 that can generate an optical signal in a format such as QPSK modulation or QAM modulation. In addition, another IQ modulator 18 may be connected to the IQ modulator 17 in parallel via the branch waveguide 19, and two IQ modulators 17 and 18 may be arranged in parallel. . In FIG. 9, reference numeral 20 denotes an electrode. This is referred to as a fifth modification.

On the other hand, the optical semiconductor element 1 may include a third SOA 21 (amplification SOA) in addition to the first SOA 4 (laser SOA) and the second SOA 5 (amplification SOA). That is, the optical semiconductor element 1 may be configured such that a total of three SOAs, one laser SOA 4 and two amplification SOAs 5 and 21, are arranged in an array.
Then, with the optical semiconductor element 1 mounted on the optical functional element 2, one IQ modulator 17 is optically connected to the second SOA 5, and the other IQ modulator 18 is optically connected to the third SOA 21. You can do that.

Further, the optical functional element 2 is provided with a polarization beam splitter (combiner) element 22 at a portion on the output end face 11 side of the output-side optical waveguide 12 to which the second SOA 5 is optically connected. An optical waveguide (silicon waveguide) 23 that is optically connected may be connected, and a polarization rotator element 24 may be provided in the optical waveguide 23.
With this configuration, the optical signals independently generated by the two IQ modulators 17 and 18 are amplified by the two SOAs, that is, the second SOA 5 and the third SOA 21, respectively. One of the two amplified optical signals has its polarization plane rotated by the polarization rotator element 24 and is polarization multiplexed with the other optical signal by the polarization beam splitter (combiner) element 22. In this way, for example, a polarization-multiplexed QPSK signal used in digital coherent communication can be generated.

  Further, a plurality of the above-described embodiments and modifications may be provided in parallel. In this case, in the above-described embodiments and modifications, a plurality of optical circuits included in the optical circuit element on the Si substrate constituting the optical functional element are provided in parallel on the same Si substrate, and InP as an optical semiconductor element is provided. A plurality of first SOAs and second SOAs included in the SOA array element may be provided in parallel on the same InP substrate.

Further, the above-described embodiment and each modified example may be provided in an optical integrated device in which a portion that functions as an optical transmitter and a portion that functions as an optical receiver are integrated. That is, a transmission / reception optical integrated device may be configured using the optical integrated device of the above-described embodiment and each modification. An optical communication apparatus provided with such an optical integrated element is an optical transceiver.
For example, as shown in FIG. 10, a transmission / reception optical integrated element (integrated transmission / reception optical device) is provided in the optical integrated element (wavelength variable laser element; laser element; a portion indicated by symbol Y in FIG. 10) of the above-described embodiment. Two IQ modulators 26 and 27 are connected to one of the output side optical waveguides 12 via a branching waveguide 25, two coherent light receivers 28 and 29 are connected to the other, and two IQ modulations are further performed. Devices 26 and 27 are connected by a polarization beam splitter (combiner) element 30, and a polarization rotator element 31 is provided between one of the two IQ modulators 26 and 27 and the polarization beam splitter (combiner) element 30. Two coherent light receivers 28 and 29 are connected by a polarization beam splitter (combiner) element 32, and one of the two coherent light receivers 28 and 29 is connected to a polarization beam splitter. Data may be provided a polarization rotator element 33 between (combiner) element 32. That is, in addition to the optical functional element 2 constituting the optical integrated element 3 of the above-described embodiment, two IQ modulators 26 and 27, two coherent light receivers 28 and 29, and two polarization beam splitter (combiner) elements are provided. 30, 32, and two polarization rotator elements 31, 33 may be integrated. This is called a sixth modification.

  The polarization beam splitter (combiner) elements 30 and 32 are also referred to as polarization multiplexing (separation) elements. Such an integrated transmission / reception optical device 3 is also referred to as an integrated transmission / reception optical device for digital coherent communication. The two IQ modulators 26 and 27, the polarization beam splitter (combiner) element 30, and the polarization rotator element 31 are collectively referred to as a transmission optical device or a transmission optical element. The two coherent light receivers 28 and 29, the polarization beam splitter (combiner) element 32, and the polarization rotator element 33 are collectively referred to as a reception optical device or a reception optical element. For this reason, the optical functional element 2 constituting the optical integrated element 3 may include a transmission optical element and a reception optical element.

Here, the two IQ modulators 26 and 27 are configured by connecting two silicon modulators (Mach-Zehnder modulators) 34 and 35 in parallel, respectively. These IQ modulators 26 and 27 are connected in parallel via a branching waveguide 36. In FIG. 10, reference numeral 37 indicates an electrode.
The two coherent light receivers 28 and 29 are each configured to include a 90 ° hybrid element 38 and a germanium light receiver 39 connected thereto. These coherent light receivers 28 and 29 are connected in parallel via the branch waveguide 40. In FIG. 10, the portion indicated by the symbol X is a crossed waveguide.

With this configuration, the output light from the wavelength tunable laser element (laser element; the portion indicated by symbol Y in FIG. 10) of the above-described embodiment is branched into two, one of which is the two IQ modulators 26. 27 is input to a portion functioning as a transmitter, and the other is input to a portion functioning as a receiver including two coherent light receivers 28 and 29.
In the portion functioning as the transmitter, the output light from the wavelength tunable laser element (laser element; the portion indicated by symbol Y in FIG. 10) is further branched into two, and then the two IQ modulators 26 and 27 provide independent QPSK signals. Convert to One of these two QPSK signals has its plane of polarization rotated by a polarization rotator element 31 and is polarization multiplexed with the other by a polarization beam splitter (combiner) element 30, and then the integrated transmission / reception optical device from the output end face 11. 3 is output as a transmission signal (optical signal) to the outside.

  On the other hand, in the part functioning as a receiver, after the output light from the wavelength tunable laser element (laser element; the part indicated by symbol Y in FIG. 10) is further branched into two, each of the two coherent light receivers 28 and 29 is provided. Is input to a 90 ° hybrid element 38. The 90 ° hybrid element 38 provided in one of the two coherent light receivers 28 and 29 receives an optical signal (received signal) input from the outside of the integrated transmission / reception optical device 3 to the input end face 41 through a polarization beam splitter ( A 90 ° hybrid element 38 that is polarized and separated by a combiner (element) 32 and is provided on the other side is polarized by a polarization beam splitter (combiner) element 32 and polarized by a polarization rotator element 33. The wavefront is rotated and input. Then, in the 90 ° hybrid element 38 provided in each of the two coherent light receivers 28 and 29, the output light from the wavelength tunable laser element (laser element; the portion indicated by Y in FIG. 10) and the received signal are mixed. Then, it is converted into an electrical signal by the germanium light receiver 39 and output.

  Further, in the above-described embodiment, the concave portion 14 is provided in the optical functional element 2, and the optical semiconductor element 2 is integrated in the concave portion 14. However, the present invention is not limited to this. For example, on the carrier such as a silicon substrate. In addition, the optical functional element and the optical semiconductor element may be integrated. In this case, for example, an opening that penetrates from the front surface side to the back surface side may be provided in the optical functional element instead of the recess, and the optical semiconductor element may be integrated in this opening.

The present invention is not limited to the configurations described in the above-described embodiments and modifications, and various modifications can be made without departing from the spirit of the present invention.
Hereinafter, additional notes will be disclosed with respect to the above-described embodiment and each modification.
(Appendix 1)
An optical semiconductor element comprising a first semiconductor optical amplifier and a second semiconductor optical amplifier, wherein both end faces where light is input and output are coated with antireflection;
A waveguide-type mirror;
A waveguide-type partial reflection mirror, an optical waveguide provided between the partial reflection mirror and the mirror, a waveguide-type wavelength filter provided in the optical waveguide and including a ring resonator, and the partial reflection An optical functional element comprising an output side optical waveguide provided between the mirror and the output end face;
The optical semiconductor element and the light are connected so that the first semiconductor optical amplifier is optically connected to the optical waveguide, and the second semiconductor optical amplifier is optically connected to the output-side optical waveguide. An optical integrated device, wherein functional devices are integrated.

(Appendix 2)
The optical integrated device according to appendix 1, wherein the mirror is provided in the optical functional device.
(Appendix 3)
The wavelength filter is a vernier type wavelength filter using two ring resonators,
The optical integrated device according to appendix 1 or 2, wherein the mirror is a loop mirror or a diffraction grating mirror.

(Appendix 4)
The wavelength filter is composed of one ring resonator and a diffraction grating mirror,
The optical integrated device according to appendix 1 or 2, wherein the mirror is the diffraction grating mirror.
(Appendix 5)
Any one of Supplementary notes 1 to 4, wherein the optical functional element includes an optical modulator provided in the output-side optical waveguide and positioned between the partial reflection mirror and the second semiconductor optical amplifier. The optical integrated device according to item 1.

(Appendix 6)
The optical integrated device according to appendix 1, wherein the mirror is provided in the optical semiconductor device.
(Appendix 7)
The mirror is a diffraction grating mirror provided in the optical semiconductor element;
The optical integrated device according to appendix 6, wherein the wavelength filter is located between the first semiconductor optical amplifier and the partial reflection mirror.

(Appendix 8)
8. The optical integrated device according to appendix 7, wherein the wavelength filter is a vernier type wavelength filter using two ring resonators.
(Appendix 9)
9. The optical integrated device according to any one of appendices 1 to 8, wherein an end face of the optical semiconductor element is the output end face.

(Appendix 10)
The optical integrated device according to any one of appendices 1 to 9, wherein the optical functional device includes a phase adjuster provided in the optical waveguide.
(Appendix 11)
The optical semiconductor element is formed on an InP substrate or a GaAs substrate,
11. The optical integrated device according to any one of appendices 1 to 10, wherein the optical functional device is formed on a Si substrate.

(Appendix 12)
The optical integrated device according to any one of appendices 1 to 11, wherein the optical functional device includes a transmitting optical device and a receiving optical device.
(Appendix 13)
An optical communication device comprising the optical integrated device according to any one of appendices 1 to 12.

DESCRIPTION OF SYMBOLS 1 Optical semiconductor element 2 Optical functional element 3 Optical integrated element 4 1st SOA
4X SOA part 5 Second SOA
6 End face of optical semiconductor element 7 Mirror 7X DBR part 8 Partial reflection mirror 9 Optical waveguide (laser side optical waveguide)
DESCRIPTION OF SYMBOLS 10 Wavelength filter 10A, 10B, 10C Ring resonator 10D Diffraction grating mirror 10X Heater 11, 11X Output end surface 12 Output side optical waveguide 13 Phase adjuster 13X Heater 14 Recessed part (terrace)
15 Optical modulator (silicon modulator; Mach-Zehnder modulator)
15X electrode 16 optical modulator (silicon modulator; Mach-Zehnder modulator)
17, 18 IQ modulator 19 Branching waveguide 20 Electrode 21 Third SOA
DESCRIPTION OF SYMBOLS 22 Polarization beam splitter (combiner) element 23 Optical waveguide 24 Polarization rotator element 25 Branch waveguide 26, 27 IQ modulator 28, 29 Coherent light receiver 30 Polarization beam splitter (combiner) element 31 Polarization rotator element 32 Polarization Beam splitter (combiner) element 33 Polarization rotator element 34, 35 Silicon modulator (Mach-Zehnder modulator)
36 branching waveguide 37 electrode 38 90 ° hybrid element 39 germanium light receiver 40 branching waveguide 41 input end face 101 n-type InP substrate 102 core layer (waveguide core layer)
103 Cladding layer 104 Contact layer 105 Semi-insulating InP layer 106 P-side electrode 107 N-side electrode 108 Passivation film 109 Diffraction grating 110 Core layer (waveguide core layer)
200 Si substrate 201, 203 SiO ₂ cladding layer 202 Si waveguide core 204 Si waveguide

Claims (10)

An optical semiconductor element comprising a first semiconductor optical amplifier and a second semiconductor optical amplifier, wherein both end faces where light is input and output are coated with antireflection;
A waveguide-type mirror;
A waveguide-type partial reflection mirror, an optical waveguide provided between the partial reflection mirror and the mirror, a waveguide-type wavelength filter provided in the optical waveguide and including a ring resonator, and the partial reflection An optical functional element comprising an output side optical waveguide provided between the mirror and the output end face;
The optical semiconductor element and the light are connected so that the first semiconductor optical amplifier is optically connected to the optical waveguide, and the second semiconductor optical amplifier is optically connected to the output-side optical waveguide. An optical integrated device, wherein functional devices are integrated.   The optical integrated device according to claim 1, wherein the mirror is provided in the optical functional device. The wavelength filter is a vernier type wavelength filter using two ring resonators,
The optical integrated device according to claim 1, wherein the mirror is a loop mirror or a diffraction grating mirror. The wavelength filter is composed of one ring resonator and a diffraction grating mirror,
The optical integrated device according to claim 1, wherein the mirror is the diffraction grating mirror.   5. The optical functional element according to claim 1, further comprising: an optical modulator provided in the output-side optical waveguide and positioned between the partial reflection mirror and the second semiconductor optical amplifier. The optical integrated device according to claim 1.   The optical integrated device according to claim 1, wherein the mirror is provided in the optical semiconductor device. The mirror is a diffraction grating mirror provided in the optical semiconductor element;
The optical integrated device according to claim 6, wherein the wavelength filter is located between the first semiconductor optical amplifier and the partial reflection mirror.   The optical integrated element according to claim 1, wherein an end face of the optical semiconductor element is the output end face.   The optical integrated device according to claim 1, wherein the optical functional device includes a transmitting optical device and a receiving optical device.   An optical communication apparatus comprising the optical integrated device according to claim 1.