JP2011003807A - Waveguide type wavelength locker and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power consumption of an optical module, and to reduce the size of the optical module.SOLUTION: This waveguide type wavelength locker includes: a semiconductor optical waveguide 105 for making light incident; a semiconductor optical waveguide 106 disposed in parallel with the semiconductor optical waveguide 105; a hollow waveguide ring filter 107 interposed between the semiconductor optical waveguide 105 and the semiconductor optical waveguide 106; a photocoupler 108a provided between a side surface of the semiconductor optical waveguide 105 and a size surface of the hollow waveguide ring filter 107; a photocoupler 108b provided between the side surface of the hollow waveguide ring filter 107 and a side surface of the semiconductor optical waveguide 106; and a photodetection area 103 connected to the semiconductor optical waveguide 106 for detecting the intensity of light made incident from the semiconductor optical waveguide 105 to the semiconductor optical waveguide 106 via the photocouplers 108a and 108b.

Description

  The present invention relates to a waveguide type wavelength locker, a wavelength locker integrated device using the same, a wavelength tunable semiconductor laser, an optical module, and a method for manufacturing a waveguide type wavelength locker.

  One information communication system that supports the current advanced information society is a wavelength division multiplexing (WDM) optical communication system capable of transmitting a large amount of information. In this method, a plurality of different wavelengths are multiplexed and transmitted as one channel in one optical fiber. The light source for the communication system needs to be able to oscillate at a wavelength determined by the system, and the oscillation wavelength requires high accuracy over a long period of time. Therefore, a wavelength locker is usually used.

  In the system, a wavelength selection filter such as an AWG (American Wire Gauge) filter is disposed as a countermeasure against crosstalk between adjacent channels. For this reason, when the wavelength is largely shifted, excess loss occurs in the wavelength selection filter. Therefore, high wavelength accuracy is required in the WDM optical communication system. The wavelength used in the WDM communication system is determined by the ITU (International Telecommunication Union) standard, and specific wavelengths of 50 GHz and 100 GHz intervals (ITU grid intervals) are used, and the wavelength accuracy is, for example, ± 5 GHz or less. There is a need.

  A wavelength locker for realizing such high wavelength accuracy is already built in a semiconductor laser (LD) module (for example, Patent Document 1). The wavelength locker is composed of a wavelength selection filter having transmission characteristics of at least a fixed period and a light receiving element that monitors the light intensity transmitted through the filter. A solid etalon is generally used for the wavelength selective filter. Further, the wavelength locker of Patent Document 1 incorporates an external light receiving element for monitoring the light output from the LD.

  The current value of the light receiving element is periodically changed by the wavelength selection filter. Wavelength locker control is possible by using this periodic characteristic. If you want to oscillate at a specific wavelength, record the current value of the light receiving element at that wavelength, and control the wavelength tunable filter or wavelength selection filter of the wavelength tunable laser so that the current value is constant. To do. This enables oscillation at a specific wavelength over a long period of time. This is maintained even when external disturbances such as environmental temperature fluctuations occur.

  Normally, the period of the wavelength selection filter is the same as the ITU grid interval. As a result, the current values of the light receiving elements can be used at substantially the same value in all of the plurality of different channels, and high wavelength accuracy can be realized in the plurality of channels.

  In addition, wavelength lockers for optical communications are constructed on a substrate whose temperature is controlled by a Peltier element to prevent wavelength shifts due to environmental temperature fluctuations, and quartz or artificial quartz solid etalon (etalon) is used as a wavelength selection filter. Is called. Quartz and artificial quartz are less susceptible to temperature fluctuations than materials such as semiconductors, and therefore wavelength shifts due to environmental temperature fluctuations can be suppressed only by temperature control based on the substrate temperature.

JP 2002-252413 A JP 2005-327881 A Japanese Patent Laid-Open No. 9-8398

  However, in recent years, there has been a demand for lower power consumption and further miniaturization of an optical module with a built-in wavelength locker.

  Although the power consumption of the entire WDM communication system is very high, the current optical module with a built-in wavelength locker requires temperature control not only for the laser but also for the wavelength locker.

  FIG. 13 shows the result of the LD oscillation wavelength dependence of the current value flowing in the light receiving element built in the optical module and monitoring the output from the semiconductor laser. FIG. 13 shows changes in the transmission spectrum of etalon. FIG. 14 shows a schematic diagram of a change in the transmission spectrum of the etalon when the temperature changes by ΔT. The transmission peak of the etalon is greatly shifted by a slight temperature change ΔT. Since this shift is large, temperature control is essential and power consumption increases. Further, when there is such a large fluctuation, the filter transmission peak in FIG. 13 is greatly shifted by the temperature change of the element due to the environmental temperature fluctuation even if the temperature control is performed. Therefore, complicated control is required to compensate for external disturbances such as environmental temperature fluctuations.

  By controlling the temperature of the etalon, power consumption is high and heat is generated. In the WDM system, a large number of modules that generate large amounts of heat are arranged, so that not only power consumption is large but also heat generation cannot be ignored. Therefore, the power consumption of the whole system becomes very high, such as a cooling system for cooling these optical modules.

  Moreover, although many light sources are arrange | positioned on the structure of a WDM communication system, space is limited. However, in the current wavelength locker system, it is necessary to use collimated light for a wavelength selective filter using a Fabry-Perot resonator such as a solid etalon. Due to the use of a collimating optical system, it is necessary to use a plurality of optical parts having a size of several millimeters such as a lens and a PD, and there is a limit to downsizing. The need to use a Peltier device to control the temperature of the etalon is one of the factors that make it difficult to reduce the size.

In a semiconductor optical waveguide as disclosed in Patent Document 2, a ring filter is used for wavelength locking to reduce the size. However, the refractive index of the semiconductor varies greatly with temperature, and is usually 2 × 10 ⁻⁴ [K ⁻¹ ]. This is over an order of magnitude higher than the materials used in solid etalon. Therefore, it is impossible to achieve both low power consumption and miniaturization of the optical module.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wavelength locker capable of realizing low power consumption and miniaturization of an optical module.

According to the present invention,
A first semiconductor optical waveguide for incident light;
A second semiconductor optical waveguide disposed in parallel with the first semiconductor optical waveguide;
A ring-shaped hollow waveguide interposed between the first semiconductor optical waveguide and the second semiconductor optical waveguide;
A first optical coupling portion provided between a side surface of the first semiconductor optical waveguide and a side surface of the hollow waveguide;
A second optical coupling portion provided between a side surface of the hollow waveguide and a side surface of the second semiconductor optical waveguide;
Receiving light that is connected to the second semiconductor optical waveguide and detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. Elements,
A waveguide-type wavelength locker is provided.

Moreover, according to the present invention,
A first semiconductor optical waveguide for incident light;
A second semiconductor optical waveguide disposed in parallel with the first semiconductor optical waveguide;
A ring-shaped hollow waveguide interposed between the first semiconductor optical waveguide and the second semiconductor optical waveguide;
A first optical coupling portion provided between a side surface of the first semiconductor optical waveguide and a side surface of the hollow waveguide;
A second optical coupling portion provided between a side surface of the hollow waveguide and a side surface of the second semiconductor optical waveguide;
Receiving light that is connected to the second semiconductor optical waveguide and detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. Elements,
A waveguide-type wavelength locker having
A third semiconductor optical waveguide connected to the first semiconductor optical waveguide and having an optical gain;
A wavelength locker integrated device is provided.

Moreover, according to the present invention,
A first semiconductor optical waveguide for incident light;
A second semiconductor optical waveguide disposed in parallel with the first semiconductor optical waveguide;
A ring-shaped hollow waveguide interposed between the first semiconductor optical waveguide and the second semiconductor optical waveguide;
A first optical coupling portion provided between a side surface of the first semiconductor optical waveguide and a side surface of the hollow waveguide;
A second optical coupling portion provided between a side surface of the hollow waveguide and a side surface of the second semiconductor optical waveguide;
Receiving light that is connected to the second semiconductor optical waveguide and detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. Elements,
A third semiconductor optical waveguide connected to the first optical waveguide;
Have
The third semiconductor optical waveguide is
A semiconductor gain section having optical gain;
A dispersive Bragg reflector sandwiching the semiconductor gain section;
A tunable semiconductor laser is provided.

Moreover, according to the present invention,
The above-mentioned wavelength tunable semiconductor laser;
An airtight package for packaging the tunable semiconductor laser;
Have
An optical module is provided in which two or more kinds of gases having different refractive indexes are mixed in the hermetic package.

Furthermore, according to the present invention,
Forming a light receiving element;
Connecting the light receiving element and the second semiconductor optical waveguide while arranging the first and second semiconductor optical waveguides to be spaced apart in parallel;
Filling the space between the first and second semiconductor optical waveguides with a high resistance layer;
Forming a ring-shaped groove in the high resistance layer;
Including
In the step of forming a ring-shaped groove in the high resistance layer,
Providing a first optical coupling portion between a side surface of the first semiconductor optical waveguide and a side surface of the ring-shaped groove;
Providing a second optical coupling portion between a side surface of the ring-shaped groove and a side surface of the second semiconductor optical waveguide;
Including
A waveguide type wavelength locker in which the light receiving element detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. A manufacturing method is provided.

  According to the present invention, it is possible to realize low power consumption and miniaturization of an optical module.

It is a typical top view which shows the waveguide type wavelength locker which concerns on 1st Embodiment. It is A-A sectional drawing of FIG. It is a figure explaining the effect of the waveguide type wavelength locker concerning a 1st embodiment. It is a figure explaining the effect of the waveguide type wavelength locker concerning a 1st embodiment. It is a typical top view which shows a waveguide type wavelength locker in 2nd Embodiment. It is sectional drawing which shows a hollow waveguide ring filter. It is sectional drawing which shows a hollow waveguide ring filter. It is a typical top view showing a waveguide type wavelength locker in a 3rd embodiment. It is a typical top view which shows a waveguide type wavelength locker in 4th Embodiment. It is a typical top view showing a waveguide type wavelength locker in a 5th embodiment. It is a typical top view showing a waveguide type wavelength locker in a 6th embodiment. It is a figure explaining a related technique. It is a figure explaining a related technique. It is a figure explaining a related technique.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(First embodiment)
FIG. 1 is a schematic plan view showing a waveguide type wavelength locker of the present embodiment. The waveguide-type wavelength locker of the present embodiment includes a semiconductor optical waveguide (first semiconductor optical waveguide) 105 that receives light, and a semiconductor optical waveguide (second semiconductor optical waveguide) disposed in parallel with the semiconductor optical waveguide 105. 106, a ring-shaped hollow waveguide (hollow waveguide ring filter) 107 interposed between the semiconductor optical waveguide 105 and the semiconductor optical waveguide 106, side surfaces of the semiconductor optical waveguide 105, and the hollow waveguide ring filter 107. An optical coupling portion (first optical coupling portion) 108a provided between the side surface and the optical coupling portion (second optical coupling portion) provided between the side surface of the hollow waveguide ring filter 107 and the side surface of the semiconductor optical waveguide 106. Optical coupling portion) 108b and the semiconductor optical waveguide 106, and the light incident on the semiconductor optical waveguide 106 from the semiconductor optical waveguide 105 via the optical coupling portions 108a and 108b. Having a light receiving region 103 for detecting the intensity.

  The wavelength locker integrated element 100 includes a gain region 102 (third semiconductor optical waveguide) having an optical gain connected to the waveguide-type wavelength locker semiconductor optical waveguide 105. The wavelength locker integrated element 100 is formed on a semiconductor substrate, and a gain medium region 101 and a non-gain medium region 104 are provided on the semiconductor substrate. A gain region 102 and a light receiving region 103 are provided in the gain medium region 101, and semiconductor optical waveguides 105 and 106 and a hollow waveguide ring filter 107 are formed in the non-gain medium region 104.

  In order to confine light in the semiconductor, the gain region 102, the light receiving region 103, and the semiconductor optical waveguides 105 and 106 are configured by surrounding a high refractive index core layer with a low refractive index layer. As the waveguide structure of the gain region 102, the light receiving region 103, and the semiconductor optical waveguides 105 and 106, an embedded structure in which a core layer is embedded with low refractive index InP or the like can be used. The thermal expansion coefficient of the substrate 203 is preferably close to the core layer and the low refractive index layer around the core layer. For example, when an InP substrate is used, a compound semiconductor such as InGaAsP / InP is used as a material.

  The hollow waveguide ring filter 107 surrounds the hollow core with a reflection surface. In this way, light is confined and propagated in the atmosphere.

  The hollow waveguide ring filter 107 can have a highly reflective film that covers at least the inner surface of the waveguide excluding the optical coupling portions 108a and 108b. For example, as shown in the cross-sectional view of FIG. 6, the bottom surface and the inner surface of the hollow waveguide ring filter 107 can be covered with a highly reflective film 607. In addition, as shown in the cross-sectional view of FIG. 7, not only the side surface of the hollow waveguide ring filter 107 but also the upper surface can be covered with a highly reflective film 707. Thereby, the waveguide loss of the hollow waveguide can be reduced while maintaining the optical coupling with the semiconductor optical waveguides 105 and 106 and realizing the operation as a ring filter. By controlling the film thickness of the highly reflective films 607 and 707, the wavelength of the transmission peak in the optical coupling portions 108a and 108b can be finely adjusted. The film thickness can be, for example, in the range of 0.1 μm to 0.5 μm, whereby the effective refractive index of the waveguide can be controlled, and the wavelength of the transmission peak can be adjusted in nanomail units. The highly reflective films 607 and 707 can be formed as a metal film or a dielectric multilayer film, and the reflectance is preferably 90% or more.

  In the gain region 102, a grating (circuit lattice) is disposed to form a DFB (Distributed Feedback) laser. The wavelength of the DFB laser can be controlled by adjusting the temperature of the gain region 102.

  Next, an example of a method for manufacturing the wavelength locker integrated element 100 will be specifically described. First, for example, a semiconductor substrate made of a compound semiconductor such as a GaAs substrate, an InP substrate, a GaN substrate, a SiC substrate, a sapphire substrate, or a ZnSe substrate is prepared.

  Next, the semiconductor optical waveguides 105 and 106 are arranged on the prepared semiconductor substrate so as to be spaced apart in parallel. At this time, the gain region 102 is connected to the semiconductor optical waveguide 105 and the light receiving region 103 is connected to the semiconductor optical waveguide 106 by the butt joint technique. Thereby, it is possible to realize a stable laser light source that is small in reflection at each butt joint connection surface and is not affected by return light.

  Specifically, a mixed crystal semiconductor layer such as InGaAsP is grown on a semiconductor substrate. First, an InP lower cladding layer is grown on the entire surface of the semiconductor device 100 on an InP substrate. Next, an active layer is grown on the entire surface of the lower cladding layer. This active layer is a multiple quantum well layer having a composition having a gain peak near the wavelength used in the laser. Next, the non-gain medium region 104 is etched to remove the active layer. Then, a non-absorbing active layer having a small light absorption composition is grown in the butt joint in the etched region. By doing so, the non-absorbing active layer is connected to the active layer. The composition of the non-absorbing active layer is a multiple quantum well layer having a wavelength composition of 1.3 μm on the shorter wavelength side than the wavelength used in the laser. Next, a compound semiconductor such as InP is grown on the mixed crystal semiconductor layer, and a gain region 102, a light receiving region 103, and semiconductor optical waveguides 105 and 106 having a high mesa structure are formed by etching. The active layer left by this etching becomes the core layer of the gain region 102 and the light receiving region 103, and the non-absorbing active layer becomes the core layer of the semiconductor optical waveguides 105 and 106.

  Next, the semiconductor optical waveguides 105 and 106 are embedded with a high resistance layer having a high resistance and a lower refractive index than that of the active layer. For the high resistance layer, for example, InP doped with iron is used.

  Next, a highly perpendicular groove is formed in a ring shape in the high resistance layer embedded between the semiconductor optical waveguides 105 and 106. This groove can be formed using, for example, the dry etching technique shown in paragraphs 0015 to 0016 of Patent Document 3. At this time, the distance from the semiconductor optical waveguides 105 and 106 and the size of the groove are set so that the optical coupling portions 108a and 108b are formed between the side surface of the semiconductor optical waveguide 105 and the side surface of the semiconductor optical waveguide 106, respectively. Control. Specifically, the depth and width of the groove can be 1 to 3 μm, respectively. By controlling the groove width, it is possible to suppress the generation of the lateral higher-order mode, for example, 2 μm. This groove becomes the hollow waveguide ring filter 107.

  FIG. 2 shows a cross-sectional view taken along the line A-A of FIG. As shown in FIG. 2, high-mesa semiconductor optical waveguides 105 and 106 are formed on a semiconductor substrate 203. The semiconductor optical waveguide 105 includes a lower cladding layer 204, a core layer 205, and an upper cladding layer 206. The semiconductor optical waveguide 106 includes a lower cladding layer 207, a core layer 208, and an upper cladding layer 209. A hollow waveguide ring filter 107 is formed beside the semiconductor optical waveguides 105 and 106. The semiconductor optical waveguides 105 and 106 are embedded with a high resistance layer 201. The distance Δd between the semiconductor optical waveguides 105 and 106 and the hollow waveguide ring filter 107 is 1 μm or less. There is no particular lower limit of Δd, and a directional coupler from the optical waveguide 105 to the hollow waveguide ring filter 107 and from the hollow waveguide ring filter 107 to the semiconductor optical waveguide 106 can be realized, and optical coupling operable as a ring filter can be realized. Good. Δd is, for example, 0.2 μm.

  The interval between transmission peaks (FSR: Free Spectral Range) in the hollow waveguide ring filter 107 is determined by the ring length, and is expressed as FSR = light velocity / (2 × effective refractive index n × length L). For example, in order to cope with an ITU grid interval of 100 GHz, the radius R of the ring filter is about 480 μm. In order to cope with the ITU grid interval of 50 GHz, the radius R is doubled to about 960 μm.

  When the highly reflective films 607 and 707 as shown in FIG. 6 and FIG. 7 are formed inside the hollow waveguide ring filter 107, a part of the element in the process of manufacturing the hollow waveguide ring filter 107 is cut out to be hollow. The transmission characteristics of the waveguide ring filter 107 are evaluated. Next, the difference between the transmission peak and the ITU grid is extracted. Based on the difference, the film thicknesses of the highly reflective films 607 and 707 are determined. By doing so, the transmission peak and the ITU grid can be matched.

  When a metal film is formed as the highly reflective films 607 and 707, for example, the metal film can be formed by vapor deposition inside the hollow waveguide ring filter 107 using an ion sputtering vapor deposition apparatus. At this time, the optical coupling portions 108a and 108b between the optical waveguides 105 and 106 and the hollow waveguide ring filter 107 are masked. By doing so, the optical coupling portions 108a and 108b can be structured so as not to have a metal film. Further, since a metal film is formed on the side surface of the hollow waveguide ring filter 107 by wraparound during sputter deposition, sputter deposition is performed for a time longer than the normal deposition time. In addition, when the upper surface of the hollow waveguide ring filter 107 is also covered with a highly reflective film 707 as shown in FIG. 7, a production technique such as MEMS (Micro Electro Mechanical Systems) can be used. For example, after the hollow waveguide ring filter 107 is provided with a highly reflective film 707 made of a metal film embedded with a dielectric such as BCB (benzocyclobutene), only the dielectric is selectively etched away by wet etching. By doing so, a highly reflective film 707 made of a metal film can be formed.

  Thereafter, electrodes (not shown) are formed in the gain region 102 and the light receiving region 103 to complete the wavelength locker integrated device 100.

  Next, the operation of the wavelength locker integrated device 100 of this embodiment will be described. A part of light (0.1 to 10% of the total light amount) emitted from the DFB laser in the gain region 102 is dropped on the semiconductor optical waveguide 105, and the optical coupling unit 108a, the hollow waveguide ring filter 107, the optical coupling unit 108b, and the semiconductor. The light is guided to the light receiving region 103 through the optical waveguide 106. Next, the light intensity is monitored in the light receiving region 103, and the temperature of the gain region is controlled so that the monitored current value becomes the current value recorded in advance. Thereby, light of a specific wavelength can be oscillated from the gain region 102.

  Next, the effect of this embodiment will be described. This waveguide-type wavelength locker has a ring-shaped hollow waveguide ring filter 107 between the optical waveguide 105 and the optical waveguide 106 arranged in parallel therewith, and passes through the optical coupling portions 108a and 108b, thereby the semiconductor optical waveguide 105. The light receiving area 103 detects the light incident on. As a result, only light that can pass through the optical coupling portions 108 a and 108 b is detected in the light receiving region 103, so that the wavelength can be locked at the transmission peak of the hollow waveguide ring filter 107. The material of the hollow waveguide core is air, and the refractive index change with temperature is small. Therefore, fine adjustment of the temperature is unnecessary, and an optical module that can be miniaturized while reducing power consumption can be realized.

  Here, the transmission characteristics of the hollow waveguide ring filter 107 will be described with reference to FIG. FIG. 3 is a diagram illustrating a result of a current value flowing through the light receiving region 103. FIG. 3 shows that the period of the hollow waveguide ring filter 107 is the same as the ITU grid interval of 100 GHz. In the waveguide type wavelength locker of this embodiment, the wavelength is locked using the transmission peak of the hollow waveguide ring filter 107 (the maximum point of the current value in FIG. 3). This is due to the following two reasons.

  One is that the optical coupling from the optical waveguide 105 to the hollow waveguide ring filter 107 is small, and the transmission peak has a narrow full width at half maximum. As an index indicating wavelength selectivity in the wavelength selection filter, there is finesse obtained by dividing the FSR by the full width at half maximum of the transmission peak. This finesse is as high as 15 or more in the hollow waveguide ring filter 107. The conventional wavelength locker uses a low finesse of about finesse 4 and uses the slope of the transmission characteristic, but the same method as the conventional one cannot be used with this high finesse characteristic.

  Another reason is that the waveguide loss of the hollow waveguide ring filter 107 is high. This is because the reflectance at the boundary between the core portion and the cladding portion of the hollow waveguide ring filter 107 is finite and there is no confinement effect in the height direction. Due to this excessive loss, wavelength control using a slope is strongly influenced by external disturbances.

  For these two reasons, wavelength lock control using the transmission peak of the hollow waveguide ring filter 107 is employed. Since the wavelength selection characteristic is high finesse, high wavelength accuracy of ± 0.5 GHz or less can be realized by matching the peak wavelength with the ITU channel.

Further, by using this hollow waveguide ring filter 107, a wavelength locker function without temperature dependency can be realized. FIG. 4 shows the results of the temperature dependence of the transmission peak in the hollow waveguide ring filter 107 (hollow ring). For reference, the results of the wavelength locker (InP), which consists of an InP cladding layer and an InGaAsP core layer, in which a ring-shaped wavelength filter is formed with a semiconductor optical waveguide, and a wavelength locker using a conventional crystal etalon are also included. Show. Note that the semiconductor optical waveguide indicated by InP in FIG. 4 has a high mesa structure similar to that of the semiconductor optical waveguides 105 and 106. The temperature dependence of the ring-shaped wavelength filter or etalon is related to both the refractive index change of the material and the shape change due to thermal expansion. In the case of the hollow waveguide ring filter 107, the change in the refractive index of the former material is hardly affected because air is used. On the other hand, with respect to the latter shape change, for example, the thermal expansion coefficient of semiconductor InP is as small as 4.5 × 10 ^−6, and the transmission peak shifts only about 0.9 GHz even when the temperature of 10 ° C. changes. This is as small as 1/100 or less in the case of a semiconductor optical waveguide. By using this hollow waveguide ring filter 107, it is not necessary to adjust the temperature of the wavelength locker. In the wavelength locker of the present embodiment, a high wavelength accuracy of ± 2 GHz or less can be realized in a DFB laser whose temperature is adjusted to ± 20 ° C.

  In this embodiment, the wavelength locker (semiconductor optical waveguides 105 and 106, the hollow waveguide ring filter 107, the light receiving region 103) and the gain region 102 are integrated on the semiconductor substrate on the semiconductor substrate, thereby saving the optical module. While realizing power, the wavelength locker can be operated more stably and the optical module can be downsized.

  Further, as shown in FIGS. 6 and 7, the high reflection films 607 and 707 are arranged on the hollow waveguide ring filter 107, and the transmission peak wavelength can be finely adjusted by adjusting the thickness thereof. In the wavelength locker of this embodiment, the filter characteristics are determined by the ring length of the hollow waveguide ring filter 107 at the time of device fabrication, and it is difficult to control the peak wavelength later. Therefore, the transmission peak wavelength can be corrected by forming the highly reflective films 607 and 707 on the hollow waveguide ring filter 107. Thereby, the yield can be improved.

(Second Embodiment)
FIG. 5 is a schematic plan view of the wavelength locker integrated device 500 of the second embodiment. The wavelength locker integrated element 500 is different from the wavelength locker integrated element 100 only in that it has a light output monitoring electrode 510 disposed on the semiconductor optical waveguide 505, and the other configuration is the same as that of the wavelength locker integrated element 100. The electrode 510 is disposed between the gain region 502 and the hollow waveguide ring filter 507 in the center. The semiconductor optical waveguide 506 corresponds to the semiconductor optical waveguide 106, the light receiving region 503 corresponds to the light receiving region 103, and the gain medium region 501 corresponds to the gain medium region 101. The non-gain medium area 504 corresponds to the non-gain medium area 104. The manufacturing method and operation are the same as in the first embodiment.

  Normally, in an optical module used in a communication system, external light receiving elements 1202 and 1203 are arranged inside as shown in FIG. 12, and the module optical output is monitored. That is, a space for the external light receiving elements 1202 and 1203 is required, leading to an increase in module size. According to the present embodiment, the external light receiving elements 1202 and 1203 that have been conventionally required can be integrated in the semiconductor element only by newly preparing the electrode 510, and the module can be miniaturized. In addition, since the optical waveguides 105 and 106 are made of a compound semiconductor, the optical waveguide loss is reduced, and the operation can be performed even by using a lossy wavelength locker such as the hollow waveguide ring filter 507. FIG. 12 illustrates an optical module that monitors the light output from the semiconductor laser 1205 via the lens 1206 using the etalon as the wavelength selection filter 1201.

  Further, in the wavelength locker integrated element 500, the absorption of the semiconductor optical waveguide 506 can be increased as long as the wavelength locker can operate as required. Thereby, optical monitoring with high sensitivity becomes possible. An optical output monitoring electrode 510 may be arranged on the side of the hollow waveguide ring filter 507 in the gain region 502.

(Third embodiment)
FIG. 8 is a schematic plan view of the wavelength locker integrated device 800 of the third embodiment. The wavelength locker integrated element 800 is an element having a photonic crystal in which a hole groove 809 is formed in the high resistance layer region 808 around the hollow waveguide ring filter 807. The hole grooves 809 are arranged with an effective length and a period of 1.55 μm of the oscillation wavelength. Other configurations are the same as those of the wavelength locker integrated device 100 of the first embodiment. The gain medium region 801 corresponds to the gain medium region 101, the gain region 802 corresponds to the gain region 102, the non-gain medium region 804 corresponds to the non-gain medium region 104, and the semiconductor optical waveguides 805 and 806 are provided. The light receiving region 803 corresponds to the light receiving region 103 and corresponds to the optical waveguides 105 and 106.

  Next, a method for manufacturing the wavelength locker integrated device 800 of this embodiment will be described. As in the first embodiment, semiconductor optical waveguides 802, 803, 805, and 806 having a high mesa structure are formed on a semiconductor substrate and embedded with a high resistance layer. Next, the hollow waveguide ring filter 807 and the hole groove 809 are collectively manufactured by etching. Thereafter, electrodes (not shown) are formed in the gain region 802 and the light receiving region 803, and the wavelength locker integrated element 800 is completed. The operation of the wavelength locker integrated element 800 is the same as that of the first embodiment.

  In the wavelength locker integrated device 800, by using a photonic crystal, the side surface of the hollow waveguide ring filter 807 can be totally reflected, and the optical waveguide loss can be greatly reduced. As a result, noise is reduced, and the wavelength locker can be controlled stably without being affected by external disturbance.

  Further, by using a photonic crystal, the waveguide can be bent sharply, and the hollow waveguide ring filter 807 can be formed in a ring shape close to a rectangle. By doing so, the coupling length of the hollow waveguide ring filter 807 can be increased, and the finesse as a wavelength selection filter can be reduced to about 10. Further, the transmitted light output point can be easily found. Furthermore, by increasing the coupling length of the hollow waveguide ring filter 807, the width of the hollow waveguide ring filter 807 can be reduced, and the element width can also be reduced. As a result, the distance between the gain region 802 and the light receiving region 803 can be narrowed, and more wavelength locker integrated elements can be manufactured from one wafer. From the above, in this embodiment, an inexpensive element can be manufactured.

(Fourth embodiment)
FIG. 9 is a plan view of an optical module including the wavelength locker integrated device 900 of the fourth embodiment. The wavelength locker of the wavelength locker integrated device 900 has substantially the same structure as that of the first embodiment, the semiconductor optical waveguides 905 and 906 correspond to the semiconductor optical waveguides 105 and 106, respectively, and the hollow waveguide ring filter 907 is a hollow waveguide. Corresponding to the waveguide ring filter 107, the gain medium region 901 corresponds to the gain medium region 101, and the non-gain medium region 904 corresponds to the non-gain medium region 104.

  In the present embodiment, the radius of the hollow waveguide ring filter 907 is 960 μm, and the FSR as the wavelength selection filter is 50 GHz. Then, by forming a grating before and after the gain region 902a, a DBR wavelength tunable laser 902 having a DBR (Distributed Bragg Reflector) sandwiching the gain region 102a is manufactured, and the gain region is formed on the light emitting side. A semiconductor amplifier 909 using the same composition as that of 902a is disposed. Further, the wavelength locker integrated element 900 is mounted on the substrate 910 on the temperature controller in the hermetic package 920.

The airtight package 920 is filled with a mixed gas obtained by mixing two or more kinds of gases having different refractive indexes. This mixed gas causes the transmission peak of the hollow waveguide ring filter 907 to coincide with the ITU grid. As the mixed gas, a gas having a small refractive index change with temperature can be used. For example, a mixed gas of an inert gas such as helium (He) gas and carbon dioxide (CO ₂ ) gas can be used. The refractive index of He gas is 1.000036, and the refractive index of CO ₂ gas is 1.000449, which are different from each other. By combining gases having different refractive indexes in this way, the refractive index can be freely adjusted between the refractive indexes. In addition, although it is a material with a small refractive index change by temperature, the material which does not become a gas at normal temperature (25 degreeC) can be heated, made into gas, and can also be mixed and used for an inert gas.

By combining gases having different refractive indexes as the gas sealed in the hermetic package 902, the hollow waveguide ring filter 907 has a variable effective resonator length as a wavelength filter. Thereby, the FSR of the wavelength filter can be adjusted. For example, by sealing with a mixed gas of He gas and CO ₂ gas, the transmission peak of the hollow waveguide ring filter 907 in the wavelength band of 1.55 μm becomes variable by 77 GHz.

  Next, a method for manufacturing the optical module of this embodiment will be described. Note that in this manufacturing method, electrical wiring is omitted for simplicity. First, the wavelength locker integrated element 900 is manufactured. The wavelength locker integrated device 900 is manufactured by growing a mixed crystal semiconductor such as InGaAsP on a semiconductor substrate as in the first embodiment. However, the same layer as the non-gain region 904 is formed by butt joint growth before and after the gain region 902a, and a grating is formed in that region. Thereby, a dispersion-type Bragg mirror 902b having no absorption is produced, and a DBR wavelength tunable laser 902 is formed. Others are manufactured by the same method as that described in the first embodiment. Next, the wavelength locker integrated element 900 is mounted on the substrate 910 in the same manner as in the production of a normal semiconductor laser module. An electrode is disposed on the dispersion type Bragg mirror 902b, and the selection wavelength of the dispersion type Bragg mirror 902b can be controlled by an injection current or a bias voltage. Next, a lens 911 is mounted on the substrate 910. At this time, a current is passed through the gain region 902 and the semiconductor optical amplifier 909 to emit light, and the lens 911 is mounted while monitoring the spread of the light transmitted through the lens 912. Thereby, the light transmitted through the lens 911 realizes good collimated light.

  Next, the substrate 910 is placed in the hermetic package 920. At this time, the substrate 910 is disposed on a temperature controller disposed in the hermetic package 920. Next, the second lens 912 and the fiber 913 are arranged outside the package 920 so that collimated light from the semiconductor element 900 on the substrate 910 enters the fiber 913. Finally, the hermetic package 920 is enclosed and hermetically sealed. At this time, the light emitted from the fiber 913 is monitored, and the light from the semiconductor element 900 is adjusted to the ITU grid. Next, a condition where the current value reaches the maximum peak in the light receiving region 903 on the semiconductor element 900 is searched while adjusting the mixing ratio of the mixed gas sealed in the package 920. The hermetic package 920 is sealed at the mixing ratio that gives the maximum peak. This completes the optical module.

  Next, the operation of the optical module of this embodiment will be described. The present optical module controls the substrate 910 at a constant temperature. This temperature is the temperature at which the package is sealed. Then, current is passed through the gain region 902a of the wavelength tunable laser 902 to cause laser oscillation. At this time, it is desirable that the value of current flowing to the gain region 902a is about 50 mA, and the gain region 902a is an unsaturated region. The oscillation wavelength of the wavelength tunable laser 902 is controlled by an injection current to the dispersion type Bragg mirror 902b. The two dispersive Bragg mirrors 902b are reflectors having periodic reflection peaks with different periods. By controlling the reflection peak wavelength of the two dispersion-type Bragg mirrors 902b by current injection, the wavelength can be controlled by the vernier effect. This is a wavelength control method similar to that of a normal DBR laser. This wavelength variable control is controlled with high accuracy using a wavelength locker. The operation of this wavelength locker is the same as that of the first embodiment.

  In the present embodiment, long-term reliability of the optical module can be improved by using an inert gas such as He gas. Further, by adjusting the medium to be hermetically sealed in the hermetic package 920, the transmission peak of the hollow waveguide ring filter 907 can be matched with the ITU grid. Therefore, the yield in module production can be greatly improved.

  Further, as shown in FIG. 6 or FIG. 7, high reflection films 607 and 707 are formed in the hollow waveguide ring filter 907, and the mixed gas composition of the hermetic package 920 is controlled while controlling the film thickness of the high reflection film. Also good. By doing so, even when the FSR of the wavelength filter is 100 GHz or more, it is possible to eliminate yield deterioration due to ring fabrication accuracy.

(Fifth embodiment)
FIG. 10 is a schematic plan view showing the wavelength locker integrated element 1000 of the fifth embodiment. In the present embodiment, the wavelength locker of the first embodiment is applied to an external resonator type wavelength tunable laser. In the wavelength locker integrated device 1000, a semiconductor optical waveguide 1030 for emitting light is arranged in parallel on a semiconductor optical waveguide 1005 corresponding to the semiconductor optical waveguide 105 of the first embodiment. A directional coupler 1015 is formed between the semiconductor optical waveguides 1005 and 1030. A gap mirror 1031 is disposed between the semiconductor optical waveguide 1030 and the gain region 1002. An external lens 1032 and an external wavelength tunable mirror 1033 are arranged on the end face side of the gain region 1002 opposite to the end face facing the gap mirror 1031. The structure of the wavelength locker is the same as that of the first embodiment. The gain medium region 1001 corresponds to the gain medium region 101, the light receiving region 1003 corresponds to the light receiving region 103, the non-gain medium region 1004 corresponds to the non-gain medium region 104, and the semiconductor optical waveguide 1006. Corresponds to the semiconductor optical waveguide 106, and the hollow waveguide ring filter 1007 corresponds to the hollow waveguide ring filter 107.

  Next, a method for manufacturing the wavelength locker integrated element 1000 will be described. As in the first embodiment, high-mesa semiconductor optical waveguides 1002, 1003, 1005, 1006, and 1030 are formed on a semiconductor substrate and embedded with a high resistance layer. Next, the hollow waveguide ring filter 1007 and the gap mirror 1031 are manufactured together by etching. The directional coupler 1015 has a structure for extracting light toward the wavelength locker at a ratio of 10: 1, for example. The rest is the same as the method described in the first embodiment.

  Next, the operation of the wavelength locker integrated element 1000 will be described. In the wavelength locker integrated element 1000, an external resonator is configured between the external wavelength variable mirror 1033 and the gap mirror 1031. A directional coupler 1015 is used on the semiconductor optical waveguide 1030 to extract part of the light oscillated in the gain region 1002. The extracted light is introduced into the light receiving region 1003 through the hollow waveguide ring filter 1007 and the semiconductor optical waveguide 1006. In the light receiving region 1003, the current value is monitored, and the temperature of the gain region 1002 is controlled so that the current value corresponds to the target oscillation wavelength. In this way, the wavelength of the emitted light is changed to the target wavelength.

  According to this embodiment, wavelength lockers can be integrated into an external resonator type wavelength tunable laser, and the module can be reduced in size and power consumption.

(Sixth embodiment)
FIG. 11 shows a sixth embodiment. FIG. 11 is a schematic plan view in which the wavelength locker of the first embodiment is applied to a DFB array type tunable laser. The semiconductor optical waveguides 1105 and 1106 correspond to the semiconductor optical waveguides 105 and 106, respectively, and the hollow waveguide ring filter 1107 corresponds to the hollow waveguide ring filter 107. As a DFB array laser, a DFB laser array composed of a plurality of DFB laser elements 1141 on a semiconductor substrate 1100, an MMI (Multimode Interference Multiplexer) region 1142 that couples the DFB laser elements 1141, and finally light And a semiconductor optical amplifier region 1143 for amplifying the signal. The semiconductor optical amplifier and the semiconductor optical path for light emission 1130 are connected without a gap mirror by butt joint bonding. The other wavelength lockers have the same structure as that of the fifth embodiment. The light receiving area 1103 corresponds to the light receiving area 1003, and the directional coupler 1115 corresponds to the directional coupler 1015.

  Next, a manufacturing method of the wavelength locker integrated element 1000 of this embodiment will be described. A grating was produced in the entire region of the DFB laser element 1141 to form a DFB laser array. As described in the first embodiment, high-mesa semiconductor optical waveguides 1130, 1105, and 1106, a semiconductor optical amplifier 1143, an MMI region 1142, a DFB laser element 1141, and a light-receiving region 1103 are collectively manufactured by etching. To do. The rest is the same as the method described in the first embodiment.

  Next, the operation of the wavelength locker integrated element 1000 of this embodiment will be described. Since the DFB laser elements 1141 have different oscillation wavelengths, the DFB laser element 1141 having a wavelength desired to be oscillated is first selected and current is injected. Other than that, the wavelength is finely adjusted according to the temperature as in the first embodiment. The operation of the wavelength locker is the same as in the first embodiment.

  In this embodiment, a wavelength locker integrated light source for a broadband wavelength tunable laser having a plurality of semiconductor lasers such as a DFB array type can be realized, and the module can be reduced in size and power consumption.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable. The present invention can be applied to all optical modules for fixedly controlling the wavelength of a WDM communication system, a measuring apparatus / inspection apparatus, and the like.

100 wavelength locker integrated element 101 gain medium region 102 gain region 103 light receiving region 104 non-gain medium region 105 first semiconductor optical waveguide 106 second semiconductor optical waveguide 107 hollow waveguide ring filter 108a first optical coupling portion 108b Second optical coupling portion 201 High resistance layer 203 Semiconductor substrate 204 Lower cladding layer 205 Core layer 206 Upper cladding layer 207 Lower cladding layer 208 Core layer 209 Upper cladding layer 500 Wavelength locker integrated element 501 Gain medium region 502 Gain region 503 Light reception Region 504 Non-gain medium region 505 First semiconductor optical waveguide 506 Second semiconductor optical waveguide 507 Hollow waveguide ring filter 510 Electrode 607 High reflection film 707 High reflection film 800 Wavelength locker integrated element 801 Gain medium region 802 Gain region 803 Light receiving area 804 Non-gain medium region 805 First semiconductor optical waveguide 806 Second semiconductor optical waveguide 807 Hollow waveguide ring filter 808 High resistance layer region 809 Hole groove 900 Wavelength locker integrated device 900 Semiconductor device 901 Gain medium region 902 Variable wavelength Laser 902a Gain region 902b Dispersive Bragg mirror 903 Light receiving region 904 Non-gain medium region 905 First semiconductor optical waveguide 906 Second semiconductor optical waveguide 907 Hollow waveguide ring filter 909 Semiconductor amplifier 909 Semiconductor optical amplifier 910 Substrate 911 Lens 912 Lens 913 Fiber 920 Airtight package 1000 Wavelength locker integrated element 1001 Gain medium region 1002 Gain region 1003 Light receiving region 1004 Non-gain medium region 1005 First semiconductor optical waveguide 1006 Second semiconductor optical Path 1007 Hollow waveguide ring filter 1015 Directional coupler 1030 Semiconductor optical waveguide 1031 Gap mirror 1032 External lens 1033 External wavelength tunable mirror 1100 Semiconductor substrate 1103 Light receiving region 1105 First semiconductor optical waveguide 1106 Second semiconductor optical waveguide 1107 Hollow waveguide Waveguide ring filter 1115 Directional coupler 1130 Semiconductor optical path 1141 DFB laser element 1142 MMI region 1143 Semiconductor optical amplifier region 1201 Wavelength selection filter 1202 External light receiving element 1203 External light receiving element 1205 Semiconductor laser 1206 Lens

Claims (9)

A first semiconductor optical waveguide for incident light;
A second semiconductor optical waveguide disposed in parallel with the first semiconductor optical waveguide;
A ring-shaped hollow waveguide interposed between the first semiconductor optical waveguide and the second semiconductor optical waveguide;
A first optical coupling portion provided between a side surface of the first semiconductor optical waveguide and a side surface of the hollow waveguide;
A second optical coupling portion provided between a side surface of the hollow waveguide and a side surface of the second semiconductor optical waveguide;
Receiving light that is connected to the second semiconductor optical waveguide and detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. Elements,
A waveguide-type wavelength locker.   The waveguide type wavelength locker according to claim 1, further comprising a semiconductor substrate on which at least the hollow waveguide and the light receiving element are integrated.   3. The waveguide-type wavelength locker according to claim 1, wherein the hollow waveguide further includes a reflective film that covers at least an inner surface of the waveguide excluding the first optical coupling portion and the second optical coupling portion. .   The waveguide type wavelength locker according to any one of claims 1 to 3, wherein the first and second semiconductor optical waveguides are formed of an InGaAsP / InP-based material. A first semiconductor optical waveguide for incident light;
A second semiconductor optical waveguide disposed in parallel with the first semiconductor optical waveguide;
A ring-shaped hollow waveguide interposed between the first semiconductor optical waveguide and the second semiconductor optical waveguide;
A first optical coupling portion provided between a side surface of the first semiconductor optical waveguide and a side surface of the hollow waveguide;
A second optical coupling portion provided between a side surface of the hollow waveguide and a side surface of the second semiconductor optical waveguide;
Receiving light that is connected to the second semiconductor optical waveguide and detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. Elements,
A waveguide-type wavelength locker having
A third semiconductor optical waveguide connected to the first semiconductor optical waveguide and having an optical gain;
A wavelength locker integrated device.   The wavelength locker integrated device according to claim 5, wherein the first, second, and third semiconductor optical waveguides all have the same structure. A first semiconductor optical waveguide for incident light;
A second semiconductor optical waveguide disposed in parallel with the first semiconductor optical waveguide;
A ring-shaped hollow waveguide interposed between the first semiconductor optical waveguide and the second semiconductor optical waveguide;
A first optical coupling portion provided between a side surface of the first semiconductor optical waveguide and a side surface of the hollow waveguide;
A second optical coupling portion provided between a side surface of the hollow waveguide and a side surface of the second semiconductor optical waveguide;
Receiving light that is connected to the second semiconductor optical waveguide and detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. Elements,
A third semiconductor optical waveguide connected to the first optical waveguide;
Have
The third semiconductor optical waveguide is
A semiconductor gain section having optical gain;
A dispersive Bragg reflector sandwiching the semiconductor gain section;
A tunable semiconductor laser. The wavelength tunable semiconductor laser according to claim 7,
An airtight package for packaging the tunable semiconductor laser;
Have
An optical module in which two or more kinds of gases having different refractive indexes are mixed in the hermetic package. Forming a light receiving element;
Connecting the light receiving element and the second semiconductor optical waveguide while arranging the first and second semiconductor optical waveguides to be spaced apart in parallel;
A step of filling a space between the first and second semiconductor optical waveguides with a high resistance layer;
Forming a ring-shaped groove in the high resistance layer;
Including
In the step of forming a ring-shaped groove in the high resistance layer,
Providing a first optical coupling portion between a side surface of the first semiconductor optical waveguide and a side surface of the ring-shaped groove;
Providing a second optical coupling portion between a side surface of the ring-shaped groove and a side surface of the second semiconductor optical waveguide;
Including
A waveguide type wavelength locker in which the light receiving element detects the light intensity of light incident on the second semiconductor optical waveguide from the first semiconductor optical waveguide via the first and second optical coupling portions. Manufacturing method.

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