JP2007134480A - Tunable light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To coincide an oscillation wavelength of a DFB laser even after a device is manufactured with a central wavelength of a transmission band of a semiconductor array waveguide lattice. <P>SOLUTION: A variable-wavelength light source 100-1 is constituted by connecting a semiconductor array waveguide lattice 120-1 having a small light loss in the device with a DFB laser array 110. An electrode 106 is provided in the array waveguide 123 of the semiconductor array waveguide lattice 120-1, and a voltage is applied to the electrode 106 whereby an electric field can be applied to a core layer of the waveguide 123 to change a transmission refractive index. In this manner, the transmission refractive index is changed, whereby even after the variable-wavelength light source 100-1 is manufactured, the oscillation wavelength of the DFB laser can be made coincident with the central wavelength of the transmission band of the semiconductor array waveguide lattice 120-1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wavelength tunable light source applied to an optical transmission system such as optical communication, optical switching, and optical information processing using an optical wavelength multiplexing system.

In addition, in the JPO electronic application system, the notation of “1” on “1” indicating the azimuth is not allowed. Therefore, in this specification (and claims), the following Table 1 is used. Each direction is written as shown in FIG. That is, the notation with “-” added on “1” is replaced with “A”.

  Currently, in order to realize large-capacity communication, research and development of optical wavelength division multiplexing (WDM) network technology that multiplexes and transmits a plurality of optical signals having different optical wavelengths (frequencies) on one optical fiber is actively conducted. Has been done. In this WDM system, it is necessary to prepare a large number of light sources having an oscillation wavelength that matches the channel wavelength (frequency) grid. However, in order to realize a highly reliable communication system, If all light sources are duplicated, the cost will be enormous. Against this background, a so-called wavelength tunable light source that can output light of any wavelength with a single semiconductor laser chip can be used as a common backup light source for these multiple light sources. Currently, research and development is actively underway to contribute to cost reduction.

  Typical examples of wavelength tunable light sources include SSG (Super Structure Grating) and DBR lasers (Non-patent Document 1) and SG (Sampled Grating) and DBR lasers (Non-patent Documents) with improved distributed Bragg reflectors (DBR). 2). Although these have the feature of having a large wavelength variable width and switching wavelengths at high speed, they still have problems in long-term reliability including wavelength stability.

  In another configuration, a light source group in which distributed feedback (DFB) lasers oscillating at different wavelengths are arranged in an array and an optical multiplexer are integrated (Non-Patent Document 3, hereinafter, wavelength). Called a variable DFB laser array). In this wavelength tunable DFB laser array, one laser to be used is selected from the DFB laser array, and light of a desired wavelength is output by tuning the oscillation wavelength according to temperature. Although this light source cannot switch the wavelength at a high speed as compared with the above-mentioned DBR type wavelength tunable light source, it uses a DFB laser with a proven track record, and therefore has excellent long-term stability that is important in a transmission system. It has the feature.

Y. Tohmori et al., “Broad-range Wavelength Tuning in DBR Lasers with Super Structure Grating (SSG)”, IEEE Photonics Technology Letters, vol. 5, No. 2, pp. 126-129, 1993 V. Jayaraman et al., “Extended Tuning Range in Sampled Grating DBR Lasers”, IEEE Photonics Technology Letters, vol. 5, No. 5, pp. 489-491, 1993 H.Oohashi et al., “46.9-nm Wavelength-Selectable Arrayed DFB Lasers with Integrated MMI Coupler and SOA”, 2001 International Conference on IndiumPhosphide and Related Materials (13thIPRM), FB1-2, pp.575-578,2001 M. Kohtoku et al., “Polarization-independent InP arrayed waveguide grating filter using deep ridge waveguide structure”, CLEO / Pacific Rim'97, pp.284-285, 1997 M. Kohtoku et al., “Packaged Polarization-Insensitive WDM Monitor with Low Loss (7.3 dB) and Wide Tuning Range (4.5 nm)”, IEEE Photonics Technology Letters, vol. 10, No. 11, pp.l614-1616, 1998 Advanced Optical Electronics Series 8 Optical Integrated Devices by Isao Kobayashi Kyoritsu Publishing Co., Ltd. J.G.Mendoza-Alvarez, “Analysis of depletion edge translation lightwave modulators”, J.of Lightwave Technology, vol.6, No.6, pp.798-808, 1988

  However, in the wavelength tunable DFB laser array, in order to widen the wavelength tunable width, the wavelength range covered by each DFB laser is expanded, that is, the temperature change amount is increased, or the number of lasers constituting the array is increased, or Combinations of these are possible.

The method of increasing the temperature change amount has a limit because it causes deterioration of the laser characteristics particularly on the high temperature side.
On the other hand, when the number of lasers is increased, the number of input ports of the optical multiplexer is inevitably increased. However, a multimode interference type (MMI) conventionally used as an optical multiplexer of a wavelength tunable DFB laser array. ) A coupler is a kind of optical star coupler. As the number of input ports increases, the coupling loss increases in principle (for example, 8 ports, the principle loss is 9 dB, 16 ports is 12 dB). This results in a problem that the optical output power of the wavelength tunable DFB laser array is lowered as a result.

  Therefore, as a method for reducing the optical multiplexing loss, it is conceivable to use an arrayed waveguide grating, which is a wavelength multiplexing / demultiplexing device, instead of the MMI coupler (in the arrayed waveguide grating, the principle loss is reduced even if the number of input ports increases. Will not increase).

  As shown in FIG. 9, the arrayed waveguide grating 900 includes an input waveguide 910, a slab waveguide 920, an arrayed waveguide 930, a slab waveguide 940, and an output waveguide 950. A detailed description of the arrayed waveguide grating 900 is described in Non-Patent Document 6.

  Even in the case of a semiconductor-based arrayed waveguide grating, the excess loss is reported to be about 3 dB (Non-Patent Document 4), and the total optical loss including the propagation loss is 6- A thing of about 8 dB is realizable. Therefore, when using about 8 or more lasers, there is a merit of using the semiconductor array waveguide grating from the viewpoint of optical loss.

  Further, the change rate of the oscillation wavelength of the DFB laser with respect to the temperature change is about 1 mm / ° C. as described in Non-Patent Document 3, and the change rate of the center wavelength of the transmission band with respect to the temperature change of the semiconductor array waveguide grating is also As in Non-Patent Document 5, it is also about 1 Å / ° C. That is, even if the oscillation wavelength of the wavelength tunable DFB laser array is tuned by changing the temperature, the center wavelength of the transmission band of the semiconductor array waveguide moves in synchronization with this (the oscillation wavelength of the DFB laser and the semiconductor are changed by the temperature change). The center wavelength of the transmission band of the arrayed waveguide grating shifts relatively, and the optical output power does not drop or the light does not come out in the worst case.) Semiconductor as an optical multiplexer on the same substrate as the DFB laser array Even when an arrayed waveguide grating is used, there is no problem in the operation of the wavelength tunable DFB laser array (Note that the rate of change of the transmission band center wavelength with respect to the temperature change of the quartz-based arrayed waveguide grating is smaller than that of the semiconductor system. It is an order of magnitude smaller and is not suitable for such use).

  However, at the time of device fabrication, it is quite difficult to completely match the oscillation wavelength of the DFB laser at a certain temperature with the transmission band center wavelength from the input port of the semiconductor array waveguide grating to which the DFB laser is connected. This is a factor that significantly reduces the yield of the wavelength tunable DFB laser array.

  The present invention has been made in view of the above problems, and its main purpose is to reduce the optical loss inside the device by using a semiconductor array waveguide grating in the optical multiplexer of the wavelength tunable DFB laser array, In addition, by providing the semiconductor array waveguide grating to be used with a trimming mechanism for the center wavelength of the transmission band, the oscillation wavelength of the DFB laser and the input port of the semiconductor array waveguide grating to which the DFB laser is connected can be obtained even after device fabrication. It is possible to perfectly match the center wavelength of the transmission band, provide a wavelength tunable light source with excellent long-term reliability, wide wavelength tunable width, high output and low power consumption for a long time.

In order to achieve such an object, the present invention described in claim 1
Each of a plurality of semiconductor laser elements having different oscillation wavelengths is connected to each input waveguide of the semiconductor array waveguide grating,
The waveguide of the semiconductor array waveguide grating has a layer structure in which a first n-type semiconductor cladding layer, a non-doped semiconductor core layer, and a second n-type semiconductor cladding layer are sequentially stacked on a semiconductor substrate,
At least a part of the first n-type semiconductor cladding layer, at least a part of the second n-type semiconductor cladding layer, or at least one of both the first and second n-type semiconductor cladding layers. A semi-insulating semiconductor layer is inserted in the part,
An electrode for applying an electric field to the semiconductor core layer through the semi-insulating semiconductor layer is formed.

The invention of claim 2 is the invention of claim 1,
The electrodes are formed on the arrayed waveguide of the semiconductor arrayed waveguide grating, and the electrodes are all different in length between the arrayed waveguides, and have a certain length between adjacent arrayed waveguides. It is characterized by being arranged differently.

The invention of claim 3 is the invention of claim 1,
The electrodes are formed on the arrayed waveguide of the semiconductor arrayed waveguide grating, and the electrodes are all the same length between the arrayed waveguides and are electrically separated between the arrayed waveguides. It is characterized by being.

The invention of claim 4 is the invention according to any one of claims 2 to 3,
In the arrayed waveguide, a portion where the electrode is arranged is a straight waveguide.

The invention of claim 5 is the invention of claim 4,
The semiconductor substrate has a (100) plane orientation, and the linear waveguide is parallel to a [0AA] orientation or a [01A] orientation.

The invention of claim 6 is the invention according to any one of claims 1 to 5,
The waveguide forming the semiconductor arrayed waveguide grating has a high mesa structure.

The invention of claim 7 is the invention according to any one of claims 1 to 6,
The semiconductor laser element is a distributed feedback laser or a distributed Bragg reflection laser.

  Since the wavelength tunable light source according to the present invention uses an arrayed waveguide grating in the optical multiplexer, even if the number of ports is increased, there is no increase in the principle loss, and this arrayed waveguide grating has the center wavelength of the transmission band. Since the trimming mechanism is provided, it is possible to provide a wavelength variable light source having a wide wavelength variable width, high output, and low power consumption with a high yield.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 shows a configuration in the case where the optical multiplexer in the conventional wavelength tunable DFB laser array is changed from an MMI coupler to a semiconductor array waveguide grating. That is, the wavelength tunable light source 100 according to the embodiment of the present invention is configured by connecting the semiconductor array waveguide grating 120 to the DFB laser array 110. The DFB laser array 110 and the semiconductor array waveguide grating 120 are formed by being integrated on the substrate 101.
The DFB laser array 110 is composed of eight (ch.1 to ch.8) DFB lasers (semiconductor laser elements), and the top DFB laser in the figure is the ch.1 in the figure. The bottom DFB laser is ch.8.
The semiconductor array waveguide grating 120 includes an input waveguide 121, a slab waveguide 122, an arrayed waveguide 123, a slab waveguide 124, and an output waveguide 125. Among the input ports of the eight input waveguides 121, the top in the figure is Input1, and the bottom in the figure is Input8. Among the output ports of the eight output waveguides 125, the top in the figure is Output1, and the bottom in the figure is Output8.

  The DFB lasers of ch.1 to ch.8 are connected in order to the input ports Input1 to Input8 of the semiconductor array waveguide grating 120 (ch.1 is input1 and ch.8 is Input8, in order). It is connected). The oscillation wavelengths of the DFB laser array 110 are designed to be 1550 nm, 1553 nm, 1556 nm, 1559 nm, 1562 nm, 1565 nm, 1568 nm, and 1571 nm, respectively, from ch. The semiconductor arrayed waveguide grating 120 also has a channel spacing of 3 nm as shown in Table 2 according to the oscillation wavelength, and has a free spectral range (FSR) of 8 channels (24 nm) or more, here 16 channels. (To reduce the difference in optical loss between the center port and the outer port, it is better to make the FSR larger to some extent).

  Assuming that both the DFB laser array 110 and the semiconductor array waveguide grating 120 can be manufactured as designed, any DFB laser from ch.1 to ch.8 can be oscillated at 25 ° C. as shown in Table 2. The output can be output from Output 4 of the output port of the semiconductor arrayed waveguide grating 120.

In order to obtain an output wavelength other than those listed above, the temperature is further changed after the DFB laser to be used is selected. Since the temperature dependence of the oscillation wavelength of the DFB laser is about 1 mm / ° C., for example, to obtain a wavelength of 1551 nm, ch.1 is first driven and the temperature is increased by 35 ° C. (from 25 ° C. to 10 ° C.). Therefore, the oscillation wavelength may be changed from 1550 nm to 1551 nm on the 1 nm long wave side.
The temperature dependence of the center wavelength of the transmission band of the semiconductor arrayed waveguide grating 120 is also about 1 mm / ° C., so the center wavelength of the transmission band from Input 1 (connected to DFB laser ch.1) at 35 ° C. is , 1551 nm.

  That is, even if temperature control is applied to obtain a desired oscillation wavelength, the center wavelength of the transmission band of the semiconductor arrayed waveguide grating 120 also moves in synchronization therewith, so that the optical output power can be varied or output depending on the set wavelength. It does not disappear (transmittance decreases when the wavelength is out of the transmission band center wavelength of the arrayed waveguide grating, and is not output when the channel spacing is exceeded).

  Therefore, even if the DFB laser array 110 and the semiconductor array waveguide grating 120 are integrated on the same substrate 101 (exposed to the same environmental temperature), they can function as the wavelength tunable light source 100 if they can be manufactured as designed. I understand that.

  If the operating temperature range is 20 ° C. to 50 ° C., ch.1 covers the wavelength 1549.5 nm to 1552.5 nm, and ch.2 covers the wavelength 1552.5 nm to 1555.5 nm. In addition, the entire DFB array 110 can cover all wavelengths from 1549.5 nm to 1573.5 nm.

However, actually, the oscillation wavelength of the DFB laser and the center wavelength of the transmission band of the semiconductor array waveguide grating 120 may deviate from the design value due to an error during device fabrication. If the amount of deviation from the design value of the center wavelength of the transmission wavelength of the DFB laser and the transmission band of the semiconductor arrayed waveguide grating 120 is the same and the relative relationship does not break, the output wavelength of the wavelength tunable light source 100 is corrected according to temperature. However, if the relative relationship is broken, the optical output power is lowered, resulting in a deterioration in the device yield.
In order to avoid this, even if the oscillation wavelength of the DFB laser and the center wavelength of the transmission band of the semiconductor array waveguide grating 120 are relatively shifted after the device is manufactured, a means for compensating for it is necessary.

  In the present invention, the method is characterized in that a mechanism capable of adjusting the transmission band of the semiconductor arrayed waveguide grating according to the oscillation wavelength of the DFB laser even after the device is manufactured is provided.

で表される。 A first embodiment of the present invention will now be described.
The center wavelength of the transmission band from the center input port to the center output port in the arrayed waveguide grating is

It is represented by

Here, λ is the center wavelength, n _eq is the equivalent refractive index of the arrayed waveguide, ΔL is the difference in length between adjacent arrayed waveguides, and m is the diffraction order. Therefore, it is shown that the center wavelength of the transmission band can be changed by changing n _eq as the characteristic of the arrayed waveguide grating.
For example, the center wavelength can be changed by about 0.08 nanometer (10 GHz) by changing the equivalent refractive index of 0.0001.

FIG. 2 shows a cross-sectional view of a waveguide structure that realizes the adjustment of the center wavelength of the transmission band of the semiconductor arrayed waveguide grating as described above.
As shown in FIG. 2A, the waveguide has a high mesa waveguide structure, and the layer structure is an n-type InP clad layer 102 (first n-type semiconductor clad layer) on an InP substrate 101. A non-doped InGaAsP core layer 103 (semiconductor core layer) having a band gap wavelength of 1.05 microns and a thickness of 0.5 microns, a semi-insulating (SI) type InP layer 104 (semi-insulating semiconductor layer), an n-type InP A clad layer 105 (second n-type semiconductor clad layer) is sequentially stacked.

  As shown in FIG. 2B, an electrode 106 is formed on the n-type InP cladding layer 105 so that an electric field can be applied to the InGaAsP core layer 103 in a part of the arrayed waveguide. The electrode 106 applies an electric field to the InGaAsP core layer 103 through a semi-insulating (SI) InP layer 104 which is a semi-insulating semiconductor layer. The electrode 107 is formed on the n-type InP cladding layer 102 and grounded.

  FIG. 3 shows a top view of the wavelength tunable light source 100-1 according to the first embodiment of the present invention. A DFB laser array 110 and an arrayed waveguide grating 120-1 with a transmission wavelength trimming function using the above-described waveguide are integrated on an InP substrate 101.

Further, the electrode 106 in the figure is short-circuited between the arrayed waveguides. That is, the same electric field is applied to the core layer 103 between the waveguides with electrodes.
The electrode 107 is in contact with the first semiconductor clad layer (n-type InP clad layer) 102 and is grounded as described above.

  In addition, electrical insulation is achieved between the waveguide portion with electrode and the waveguide portion without electrode by separation grooves 131 and 132 formed by removing a part of the n-type InP cladding layer 105 by etching.

  As a result, an electric field can be efficiently applied only to the core layer 104 of the waveguide portion with electrodes. Moreover, the waveguide part with an electrode is a straight line, and is arranged to be parallel to the [0AA] direction or the [01A] direction.

で表される屈折率変化を誘起する（非特許文献７参照）。 FIG. 4 shows a band diagram when a negative bias V _b is applied to the electrode 106. As shown in FIG. 4, since the SI type InP layer 104 works as an electron blocking layer, no current flows, and it can be seen that an electric field is efficiently applied to the InGaAsP core layer 103. At this time, the InGaAsP core layer 103 has an electric field E _b (= V _b / core layer) in a direction perpendicular to the substrate ([100] direction) due to the Pockels effect.

Is induced (see Non-Patent Document 7).

Here, n ₀ is the refractive index of the material, and γ ₄₁ is the Pockels constant. The + sign indicates a case where light propagates parallel to the [0AA] direction, and the-sign indicates a case where light propagates parallel to the [01A] direction. The Pockels constant takes a negative value.
Therefore, if the waveguide portion with electrodes is arranged in parallel to the [0AA] direction, the refractive index change becomes negative due to the application of an electric field, and if arranged in parallel to the [01A] direction, the refractive index change becomes positive. (Here, the description is based on the (100) substrate, but the same applies to the (001) substrate. The [100] direction is the [001] direction, the [0AA] direction is [110], and the [01A] direction is This effect can only be applied to the TE mode, but there is no problem because the DFB laser also oscillates in the TE mode.

FIG. 5 shows the relationship between adjacent arrayed waveguides in FIG. L _{e, i + 1} , L _{e, i} are the lengths of the waveguides with electrodes, L _{0, i + 1} , L _{0, i} are the lengths of the waveguides without electrodes, and n ₁ is the electric field application in the waveguides with electrodes. Where n ₀ is the equivalent refractive index of the electrodeless waveguide.

と変形される。右辺第一項は、無電界時の透過帯域の中心波長を示しており、第二項は、電界印加による中心波長の変化量を示している。 The general expression for the phase matching condition of the arrayed waveguide grating is

And transformed. The first term on the right side shows the center wavelength of the transmission band when there is no electric field, and the second term shows the amount of change in the center wavelength due to the electric field application.

For example, consider the case where the linear waveguide portion with electrodes is arranged in parallel to the [0AA] direction. In this case, the refractive index change of the InGaAsP core layer 103 is negative according to the equation (2) with respect to the negative bias V _b . Therefore, (n ₁ −n ₀ ) is negative when an electric field is applied. Therefore, when ΔL _e is negative (the waveguide with electrode becomes shorter as the array waveguide becomes longer by ΔL), the transmission band center wavelength of the semiconductor array waveguide grating 120-1 by the electric field application It can be shifted to the long wave side compared to sometimes. Therefore, when the transmission band center wavelength of the semiconductor arrayed waveguide grating 120-1 is shifted to the short wavelength side with respect to the oscillation wavelength of the DFB laser, the compensation range is obtained.

  However, it is not always shifted to the short wave side after the device is manufactured. However, this problem can be avoided if a plurality of output ports of the semiconductor arrayed waveguide grating 120-1 are prepared. That is, for example, even if the oscillation wavelength of the DFB laser is shifted to the long wave side with respect to the output port Output 4 of the semiconductor arrayed waveguide grating 120-1, the output port Output 5 is shifted to the short wave side. Therefore, the output waveguide of the element may be determined as Output 5 and finely adjusted so as to maximize the output by applying an electric field.

When ΔL _e is positive (the length of the waveguide with electrode increases as the length of the arrayed waveguide increases by ΔL), the transmission band center wavelength of the semiconductor arrayed waveguide grating 120-1 is reversed by applying an electric field. It can be shifted to the short wave side compared to when no electric field is applied. In this case as well, a plurality of output ports of the semiconductor arrayed waveguide grating 120-1 are prepared, and an output port whose transmission band center wavelength is shifted to the long wave side with respect to the oscillation wavelength of the DFB laser may be used. Fine adjustments may be made to maximize the output.

The same argument holds when the linear waveguide with electrodes is arranged in parallel to the [01A] direction. The difference from the case of the [0AA] direction is that the refractive index of the InGaAsP core layer 103 with respect to a negative bias. Since the change is positive from the equation (2), the direction in which the center wavelength of the transmission band changes is opposite to the negative bias. As can be seen from the equation (4), when ΔL _e is increased, the refractive index change can be reduced, in other words, the applied electric field can be reduced.

  Another major feature of the present embodiment is that there is no p-type layer in the layer structure of the semiconductor arrayed waveguide grating 120-1. The p-type layer has a large light absorption due to the valence band interband transition, and a relatively large device such as the semiconductor array waveguide grating 120-1 involves a large propagation loss. End up. This means that even if the optical array loss is reduced by using the semiconductor array waveguide grating 120-1 in the optical multiplexer, the merit cannot be maximized. However, since this embodiment does not use such a p-type layer that causes an increase in optical loss, a high-output wavelength variable light source can be obtained as a result.

Next, an outline of a manufacturing method of this example will be described with reference to FIGS. In this example, an SI buried structure DFB laser and a semiconductor array waveguide grating are integrated.
First, an active layer of a DFB laser is grown on an n-type InP substrate. Thereafter, after forming a grating (diffraction grating), a p-type InP cladding layer and a contact layer are grown (FIG. 6A).

  Next, the DFB laser array part is left and the active layer of the DFB laser is removed by etching, and the core layer of the arrayed waveguide grating is regrown (FIG. 6B).

Subsequently, the DFB laser part is mesa processed for embedding. (FIG. 6C).
Then, buried regrowth is performed in the SI type InP and n type InP layers. At this time, in the arrayed waveguide grating, an SI type InP layer and an n type InP clad layer (second semiconductor clad layer) functioning as a current blocking layer are laminated on the core layer (FIG. 6D). )).

Further, after removing n-type InP of the DFB laser part by etching, a high mesa waveguide of the arrayed waveguide grating part is formed (FIG. 6E).
Finally, the device is completed when electrodes are formed.

The structure of the DFB laser is not limited to the SI buried structure, but may be a pn buried type (however, in an arrayed waveguide grating, a p-type InP layer for pn embedding once laminated on the core layer) It is necessary to remove the n-type InP layer by etching and restack the SI-type InP layer), and the ridge structure may be used instead of the buried structure.
Further, it is not necessary to be a DFB laser, and it may be a distributed Bragg reflection type (DBR type) semiconductor laser.

  The core layer of the semiconductor arrayed waveguide grating has been described as a bulk, but may have a quantum well structure. Further, although the SI type InP layer 104 is inserted between the InGaAsP core layer 103 and the n type InP of the second semiconductor clad layer 105, the n type InP of the InGaAsP core layer 103 and the first semiconductor clad layer 102 is inserted. The same effect can be obtained even if it is inserted between them (however, the direction of the applied electric field must be reversed).

Further, a structure in which a contact layer such as an InGaAs layer or an InGaAsP layer is inserted between the electrodes 106 and 107 and the semiconductor in order to reduce the contact resistance may be employed.
If the n-type substrate 101 is used as the semiconductor substrate as in this embodiment, the electrode 107 in FIG. 3 can be formed on the surface of the InP substrate.

  In this embodiment, an InGaAsP / InP semiconductor material is used for explanation. However, the present invention is not limited to this material system, and other compound semiconductors may be used.

  As described above, the semiconductor arrayed waveguide grating 120-1 has a structure in which the center wavelength of the transmission band can be adjusted by applying a voltage even after the device is manufactured. Therefore, even if the oscillation wavelength of the DFB laser of the DFB laser array 110 and the center wavelength of the transmission band of the semiconductor array waveguide grating 120-1 are relatively shifted, the compensation can be performed, and the long-term reliability is excellent. A wavelength tunable light source having a wide wavelength tunable width, high output, and low power consumption can be provided with high yield.

  Example 2 and Example 1 differ only in the way of arranging the electrodes of the semiconductor arrayed waveguide grating. Therefore, only the semiconductor array waveguide grating according to the second embodiment will be described below.

FIG. 7 is a top view of the wavelength tunable light source 100-2 according to the present embodiment. An electrode 106 is disposed on a part of each arrayed waveguide 123, and the length thereof is the same between the arrayed waveguides. The electrodes 106 are electrically separated between the arrayed waveguides, and can be applied with independent electric fields.
The electrode 107 is in contact with the first semiconductor clad layer (n-type InP clad layer) 102 and is grounded. In addition, electrical insulation is also achieved between the waveguide portion with electrode and the waveguide portion without electrode by separation grooves 131 and 132 formed by removing a part of the n-type InP cladding layer 105 by etching. .

  As a result, an electric field can be efficiently applied only to the core layer 104 of the waveguide portion with electrodes. Moreover, the waveguide part with an electrode is a straight line, and is arranged to be parallel to the [0AA] direction or the [01A] direction.

と変形される。 Here, the relationship between adjacent array waveguides is shown in FIG. L _e is the length of the waveguide with electrode, L _{0, i + 1} , L _{0, i} is the length of the waveguide without electrode, and L _{0, i + 1} −L _{0, i} = ΔL (> 0) And N _{i + 1} is the equivalent refractive index when the voltage V _{b, i + 1 is} applied to the (i + 1) th waveguide with an electrode, and n _i is the voltage V _{b, This is} the equivalent refractive index when _{i is} applied, and n ₀ is the equivalent refractive index of the waveguide without electrode. When the general formula of the phase matching condition of the arrayed waveguide grating of the present embodiment is shown,

And transformed.

The first term on the right side shows the center wavelength of the transmission band when there is no electric field, and the second term shows the amount of change in the center wavelength due to the electric field application.
For example, considering the case where the linear waveguide portion with electrodes is arranged in parallel to the [0AA] direction, the change in the refractive index of the InGaAsP core layer 103 with respect to the negative bias (V _b <0) Become negative. Therefore, if the bias value is increased as the arrayed waveguide becomes longer by ΔL, (| V _{b, i + 1} |> | V _{b, i} |, that is, V _{b, i + 1} <V _{b, i} ), (N _{i + 1} −n _i ) is negative, the center wavelength of the transmission band can be changed to the short wave side.
Conversely, if the bias value is decreased as the arrayed waveguide becomes longer by ΔL, (| V _{b, i + 1} | <| V _{b, i} |, that is, V _{b, i + 1} > V _{b, i} ) Since (n _{i + 1} −n _i ) is now positive, the center wavelength of the transmission band can be changed to the long wave side.

  The same argument holds when the linear waveguide with electrodes is arranged in parallel to the [01A] direction, because the change in the refractive index of the InGaAsP core layer 103 is positive from the equation (2) with respect to a negative bias. When the bias value is increased as the array waveguide becomes longer by ΔL, the transmission band center wavelength changes to the long wave side, and when the bias value is reduced, it changes to the short wave side. That is, the difference from the [0AA] direction is that the direction in which the transmission band center wavelength changes is reversed.

  As described above, the semiconductor arrayed waveguide grating 120-2 has a structure in which the center wavelength of the transmission band can be adjusted by applying a voltage even after the device is manufactured. Therefore, even if the oscillation wavelength of the DFB laser of the DFB laser array 110 and the center wavelength of the transmission band of the semiconductor array waveguide grating 120-2 are relatively deviated, the compensation can be performed, and the long-term reliability is excellent. A wavelength tunable light source having a wide wavelength tunable width, high output, and low power consumption can be provided with high yield. The present embodiment has a feature that the transmission band center wavelength of the semiconductor arrayed waveguide grating 120-2 can be adjusted to both the long wavelength side and the short wavelength side.

1 is a structural diagram showing a wavelength tunable DFB laser array using a semiconductor array waveguide grating. Sectional drawing which shows the waveguide structure of the arrayed-waveguide grating | lattice concerning the Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows the wavelength variable light source concerning Example 1 of this invention. Explanatory drawing which shows the band diagram at the time of an electric field application. Explanatory drawing explaining the structure of the arrayed waveguide part concerning Example 1 of this invention. Explanatory drawing which shows the preparation methods of the wavelength variable light source concerning Example 1 of this invention. The block diagram which shows the wavelength variable light source concerning Example 2 of this invention. Explanatory drawing explaining the structure of the arrayed waveguide part concerning Example 2 of this invention. The block diagram which shows an arrayed-waveguide grating | lattice.

Explanation of symbols

100, 100-1, 100-2 Variable wavelength light source 101 InP substrate 102 n-type InP cladding layer (first semiconductor cladding layer)
103 Non-doped InGaAsP core layer (semiconductor core layer)
104 Semi-insulating (SI) InP layer (semi-insulating semiconductor layer)
105 n-type InP cladding layer (second semiconductor cladding layer)
106, 107 electrode 110 DFB laser array 120, 120-1, 120-2 semiconductor array waveguide grating 121 input waveguide 122, 124 slab waveguide 123 array waveguide 125 output waveguide 131, 132 separation groove

Claims (7)

Each of a plurality of semiconductor laser elements having different oscillation wavelengths is connected to each input waveguide of the semiconductor array waveguide grating,
The waveguide of the semiconductor array waveguide grating has a layer structure in which a first n-type semiconductor cladding layer, a non-doped semiconductor core layer, and a second n-type semiconductor cladding layer are sequentially stacked on a semiconductor substrate,
At least a part of the first n-type semiconductor cladding layer, at least a part of the second n-type semiconductor cladding layer, or at least one of both the first and second n-type semiconductor cladding layers. A semi-insulating semiconductor layer is inserted in the part,
An electrode for applying an electric field to the semiconductor core layer through the semi-insulating semiconductor layer is formed.   The electrodes are formed on the arrayed waveguide of the semiconductor arrayed waveguide grating, and the electrodes are all different in length between the arrayed waveguides, and have a certain length between adjacent arrayed waveguides. The tunable light source according to claim 1, wherein the tunable light sources are arranged differently.   The electrodes are formed on the arrayed waveguide of the semiconductor arrayed waveguide grating, and the electrodes are all the same length between the arrayed waveguides and are electrically separated between the arrayed waveguides. The tunable light source according to claim 1, wherein   The wavelength tunable light source according to any one of claims 2 to 3, wherein a portion of the arrayed waveguide where the electrodes are arranged is a straight waveguide. The wavelength tunable light source according to claim 4, wherein the semiconductor substrate has a (100) plane orientation, and the linear waveguide is parallel to a [0AA] orientation or a [01A] orientation.
However, each direction is written as shown in the table below.

  6. The wavelength tunable light source according to claim 1, wherein the waveguide forming the semiconductor arrayed waveguide grating has a high mesa structure.   The wavelength tunable light source according to any one of claims 1 to 6, wherein the semiconductor laser element is a distributed feedback laser or a distributed Bragg reflection laser.

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