JP5947731B2 - Multi-channel laser array light source - Google Patents

Description

  The present invention relates to a multi-channel laser array light source. More specifically, the present invention relates to a multi-channel laser array light source that enables a laser array chip in a multi-channel optical transmitter to be driven without signal degradation due to crosstalk.

  A communication light source is a fundamental component for realizing a large-capacity optical communication network. With the recent trend of increasing communication capacity, there is a need for a communication light source that is compact and compatible with multi-channel technology. In order to realize a small multi-channel light source, it is necessary to use a multi-channel laser array chip or, if possible, a multi-channel laser array chip monolithically integrated including an optical multiplexer.

  FIG. 1 is a diagram showing a configuration of a conventional single channel direct modulation DFB laser light source. The distributed feedback (DFB) laser light source is a light source generally used for a multi-channel laser array light source at present. FIG. 1B is a top view of the subcarrier 1 on which the laser chip 103 is mounted, and FIG. 1A is a side view. Since it is a single channel light source, a single laser chip 103 including at least one laser element is arranged on the subcarrier 1 provided with the wiring board. Termination resistor 106 is incorporated in high-frequency signal line 105 on subcarrier 1. The end of the high-frequency signal line 105 on the subcarrier 1 and the laser chip 103 are connected to each other using a wire 104. The bottom surface of the laser chip 103 is a ground surface, and the bottom surface of the laser substrate is in contact with the subcarrier 1.

  FIG. 2 is a diagram showing a configuration of a DFB laser array light source in which four single-channel DFB laser light sources and an optical multiplexer are integrated. FIG. 2A shows the top surface of the laser array chip 2 alone. FIG. 2B shows a top view of the entire array light source incorporating a chip, and FIG. 2C is a side view of the short side of the array light source. As shown in FIG. 2 (a), the laser array chip 2 in this configuration includes four laser elements of the single channel light source of FIG. 1, and a direct channel in which four channels are integrated by a multiplexer 8 on the chip. This is a modulated DFB laser array chip. Further, as shown in FIG. 2B, the laser array light source employs an aerial wiring structure in which the laser array chip 2 and the high-frequency wiring board 5 are arranged on the subcarrier 1. In this structure, support portions 6 a and 6 b are disposed at both ends of the subcarrier 1, and the high-frequency wiring board 5 is fixed separately from the subcarrier 1. The laser array chip 2 is disposed on the subcarrier 1, and the space between the subcarrier 1 and the high frequency wiring board 5 is hollow. In order to connect the high-frequency wiring board 5 and the laser array chip 2 as close as possible, an aerial wiring structure is applied.

  FIG. 3 is a diagram illustrating an aerial wiring structure in a laser array light source. 3A is a side view seen from the direction of the arrow A in FIG. 2B, and FIG. 3B is a side view seen from the direction of the arrow B in FIG. 2B. FIG. It should be noted that both (a) and (b) of FIG. 3 are enlarged views of the portion where the aerial wiring is made, and the dimensions of the respective axes are not drawn proportionally and faithfully. . As shown in FIG. 3A, the gold wire 3 is wired from the end of the high frequency wiring on the high frequency wiring board 5 onto the DFB laser electrode 4 of the laser array chip 2 having a different height. The laser array chip 2 is connected to the ground via the subcarrier 1 on the bottom surface of the chip 2. The high-frequency wiring board 5 is connected to the ground via the wiring board support portions 6a and 6b and further via the subcarrier 1. As shown in FIG. 3B, the laser array chip 2 is located at the center of the long side of the subcarrier 1, and the upper portion of the laser array chip 2 is hollow.

JP 2011-228468 A

W. Kobayashi et al, “40-Gbps Direct modulation of 1.3-mm InGaAlAs DFB laser in compact TO-CAN package”, in Proc. OFC, 2011, OWD2.

  However, when a laser array light source is configured as shown in FIG. 3, in a miniaturized laser array chip, the interval between lasers in each channel becomes very narrow. For this reason, there is a problem that electrical crosstalk and thermal crosstalk are large between adjacent channels. Since the substrate of the laser array chip 2 has a resistance value that cannot be ignored, there is a potential difference between the bottom surface of the laser array chip 2 and the lower cladding layer directly below the laser device formed on the chip surface. Occurs. The lasers in each channel are very close together and have a generally common impedance between each laser device and the bottom of the chip. For this reason, the device current accompanying the operation of each channel affects the ground level of the laser device of the other channel, and the ground potential in the lower cladding layer of a certain channel varies according to the operating condition of the other channel.

  Further, the heat generated in each channel during the laser operation is transmitted to the adjacent channel, so that the temperature of the laser active layer rises and the laser oscillation wavelength shifts.

  The present invention has been made in view of such problems, and the invention suppresses signal degradation due to crosstalk between channels and ensures thermal isolation between adjacent laser channels to oscillate the laser. An object of the present invention is to realize a multi-channel laser array light source capable of stable operation by suppressing wavelength shift. A method for manufacturing a multi-channel laser array light source is also provided.

In order to achieve such an object, the present invention has a layer structure including at least a semiconductor substrate, a lower cladding layer, a core layer, and an upper cladding layer, and converts an electrical signal into an optical signal. A plurality of optical functional elements, and one or more ground electrodes, each of which is disposed at least partially between two adjacent optical functional elements, and at least of the semiconductor substrate or the lower cladding layer A laser array chip including one or more ground electrodes that are in direct contact with and electrically connected to each other, and two portions of the ground electrode are disposed between two adjacent ones of the plurality of optical functional elements And the portions on both sides of one optical functional element constitute an integrated ground electrode surrounding the one optical functional element on the laser array chip surface, and the one light The integrated ground electrode of the active element and the integrated ground electrode of the other optical functional element are not connected on the laser array chip surface, and are electrically connected only through the semiconductor substrate or the lower cladding layer. it is a multi-channel laser array light source, characterized in that connected to. The ground electrode corresponds to the comb-type ground electrode in the first embodiment.
Preferably, the plurality of optical functional elements include a laser array. In the above layer structure, the lower cladding layer may be constituted by a part of the substrate. The integrated ground electrode surrounding one optical functional element corresponds to the U-shaped ground electrode in the second and third embodiments.

The invention of claim 2 has a layer structure including at least a semiconductor substrate, a lower clad layer, a core layer, and an upper clad layer, and a plurality of optical function elements for converting an electric signal into an optical signal, and the plurality of optical function elements A comb-shaped ground electrode, at least a part of which is disposed between two adjacent ones of the first and second electrodes, and is in direct contact with and electrically connected to at least one of the semiconductor substrate and the lower cladding layer A chip mounting ground electrode is formed on the upper surface, a ground electrode electrically connected to the chip mounting ground electrode is formed on the lower surface, and the laser array chip is disposed on the chip mounting ground electrode. Subcarriers, a plurality of signal wirings for guiding the electrical signals, a high-frequency wiring board having a ground electrode, and the laser array Electrical connection means (wire) for directly connecting between the comb-shaped ground electrode of the chip and at least one of the chip-mounted ground electrode of the subcarrier or the ground electrode of the high-frequency wiring board. Is a multi-channel laser array light source .

According to a third aspect of the present invention, in the laser array light source according to the first aspect, a chip mounting ground electrode is formed on the upper surface, and a ground electrode electrically connected to the chip mounting ground electrode is formed on the lower surface. A subcarrier on which the laser array chip is disposed, a high-frequency wiring board having a plurality of signal wirings and a ground electrode for guiding the electrical signal, and an electrical connection between the laser array chip, the subcarrier and the high-frequency wiring board And a general connection means. The electrical connection means corresponds to, for example, a wire made of a metal material such as gold or other conductive material.

The invention according to claim 4, in the laser array light source according to claim 2 or 3, and the chip mounting ground electrode of the sub-carrier, between the ground electrode of the laser array chip, in at least one position, electrical It is electrically connected by connecting means.

A fifth aspect of the present invention, the laser array light source according to claim 2 or 3, wherein said ground electrode on the high frequency circuit board, between the ground electrode of the laser array chip, electrically by an electrical connection means It is connected.

  A sixth aspect of the present invention is the laser array light source according to any one of the first to fifth aspects, wherein the layer structure has a lower resistivity than the semiconductor substrate, which is disposed immediately below the lower cladding layer. The ground electrode is in contact with the low resistivity layer.

  According to a seventh aspect of the present invention, in the laser array light source according to any one of the first to fifth aspects, an optical multiplexer that multiplexes optical signals output from the respective optical functional elements into one optical path is formed on the laser array chip. It is characterized by being.

  The invention according to claim 8 is the laser array light source according to any one of claims 1 to 5, wherein the optical functional element is a semiconductor distributed feedback laser (DFB laser), or a DFB laser and an electroabsorption optical modulator (EA modulation). ).

  Another aspect of the present invention has a layer structure including at least a semiconductor substrate, a lower clad layer, a core layer, and an upper clad layer, and a plurality of optical functional elements that convert electrical signals into optical signals, and the plurality of optical functions One or more ground electrodes, each of which is at least partially disposed between two adjacent elements, and is in direct contact with and electrically connected to at least one of the semiconductor substrate and the lower cladding layer. A multi-channel laser array light source including a laser array chip including one or more ground electrodes, wherein a chip mounting ground electrode is formed on an upper surface and electrically connected to the chip mounting ground electrode on a lower surface Mounting the laser array chip on a subcarrier on which a ground electrode is formed; and A step of connecting a land electrode and the chip-mounted ground electrode on the subcarrier by an electrical connection means; and a high-frequency wiring board having a plurality of signal wirings and a ground electrode for guiding the electrical signal on the subcarrier. And a step of connecting the ground electrode of the high-frequency wiring board and the chip-mounted ground electrode on the subcarrier by means of an electrical connection means. It is a method of producing.

  In the above method invention, the method may further comprise a step of connecting the DC wiring formed on the subcarrier and the semiconductor distributed feedback laser (DFB laser) electrode on the laser array chip by an electrical connection means. .

  As described above, according to the present invention, it is possible to perform stable operation by suppressing signal deterioration due to crosstalk between channels and ensuring thermal isolation between adjacent channels to suppress a shift in laser oscillation wavelength. A multi-channel laser array light source and a method for manufacturing a multi-channel laser array light source can be realized.

FIG. 1 is a diagram showing a configuration of a conventional single-channel direct modulation DFB laser light source. FIG. 2 is a diagram showing a configuration of a DFB laser array light source in which four single-channel DFB laser light sources and an optical multiplexer are integrated. FIG. 3 is a diagram illustrating an aerial wiring structure in a laser array light source. FIG. 4 is a diagram showing the structure of a DFB laser array chip having a comb-shaped ground electrode used in the laser array light source of the present invention. FIG. 5 is a diagram showing the configuration of the laser array light source of the present invention. FIG. 6 is a diagram for explaining the ground connection of the laser array light source of the present invention. FIG. 7 is a diagram illustrating a result of simulating a difference in crosstalk between channels due to the presence or absence of a ground wire between signal lines of each channel. FIG. 8 is a diagram illustrating a BER characteristic measurement system of the laser array light source according to the first embodiment. FIG. 9 is a diagram showing a BER characteristic measurement system of a laser array light source without a comb-shaped ground electrode and a ground wire manufactured for comparison. FIG. 10 is a diagram showing the configuration of the EADFB laser array chip used in Embodiment 2 of the present invention. FIG. 11 is a diagram showing a configuration of a laser array light source of Example 2 using an EADFB laser array chip. FIG. 12 is a diagram illustrating a measurement system configuration of the BER characteristic of the laser array light source according to the second embodiment. FIG. 13 is a diagram showing a BER characteristic measurement system of a laser array light source without a U-shaped ground electrode and a ground wire manufactured for comparison. FIG. 14 is a diagram showing a configuration of a direct modulation DFB laser array chip used in the laser array light source according to the third embodiment of the present invention. FIG. 15 is a diagram showing a configuration of a laser array light source of Example 3 using a direct modulation DFB laser array chip. FIG. 16 is a diagram showing a configuration of a laser array light source according to the third embodiment of the present invention viewed from the side. FIG. 17 is a diagram illustrating a measurement system configuration of the BER characteristic of the laser array light source according to the third embodiment. FIG. 18 is a view showing a BER characteristic measurement system of a laser array light source having no U-shaped ground electrode and high-frequency wiring board ground prepared for comparison.

  The present invention forms a ground electrode formed so as to surround and separate each laser device of a laser array light source, and to the ground of one or more other substrates constituting the laser array light source with respect to the ground electrode. This is characterized in that a new ground path of the laser device of each channel is formed by forming the electrical connection. That is, the laser array light source of the present invention has a layer structure including at least a semiconductor substrate, a lower cladding layer, a core layer, and an upper cladding layer, and a plurality of optical functional elements that convert an electrical signal into an optical signal, One or more ground electrodes, each of which is disposed at least partially between two adjacent ones of the optical functional elements, in direct contact with at least one of the semiconductor substrate and the lower cladding layer, A multi-channel laser array light source comprising a laser array chip including one or more ground electrodes connected to the. The optical functional element described above is an optical device that can output an optical signal and can convert an electric signal as a change in the amplitude, phase, etc. of the optical signal, and can be a laser element, for example.

FIG. 4 is a diagram showing the structure of a DFB laser array chip in which a multiplexer having a comb-shaped ground electrode structure used in the laser array light source of the present invention is integrated. 4A is a top view of the chip 22, and FIG. 4B is a cross-sectional view taken along line AA ′. The laser array chip 22 includes four laser elements 23. A comb-shaped ground electrode 24 is formed so as to surround the periphery of each laser element. Laser light from the optical waveguide from the laser element 23 of each channel is multiplexed by the optical multiplexer 25.

  The cross-sectional view of FIG. 4B includes laser elements for two channels. The laser array chip 22 is configured by forming a laser element on a semiconductor substrate 29 such as an n-InP substrate. In the semiconductor substrate 29, a lower clad layer is formed by the substrate itself, and on the lower clad layer 29, a core layer 28 that operates as an active layer and an n-InP upper clad layer 27 are configured. Dielectric insulation layers 26 are formed on both sides of the core layer 28. In the present invention, a comb-shaped ground electrode 24 is formed on the dielectric insulating layer 26 between adjacent laser elements. The comb-shaped ground electrode is connected to the lower cladding layer 29 at the intermediate point of the element.

  FIG. 5 is a diagram showing the configuration of the laser array light source of the present invention. The laser chip array 22 shown in FIG. 4 is mounted. 5A is a laser chip array, FIG. 5B is a top view of the entire array light source, and FIG. 5C is a side view seen from below the top view of FIG. 5B. It is. The configuration of the laser array light source of the present invention shown in FIG. 5B is generally similar to the configuration of the conventional laser array light source shown in FIG. That is, an aerial wiring structure in which the laser array chip 22 and the high-frequency wiring board 30 are arranged on the subcarrier 21 is used. Support portions 31 a and 31 b are disposed at both ends of the subcarrier 21, and the high-frequency wiring board 30 is fixed apart from the subcarrier 21. The laser array chip 22 is disposed on the subcarrier 21, and the space between the subcarrier 21 and the high frequency wiring board 30 is hollow.

  FIG. 6 is a diagram for explaining the ground connection of the laser array light source of the present invention. FIG. 6A is a side view of the long side of the subcarrier of FIG. 5B as viewed from the right side, and is a conceptual diagram in which the vicinity of one channel is enlarged. FIG. 6B is a side view of the short side of the subcarrier of FIG. 5B, and is a cross-sectional view including the comb-shaped ground electrode 24. As shown in FIGS. 6A and 6B, the end portion 33 of the high frequency signal line of the high frequency wiring board 30 is connected to the laser electrode 23 of the laser array chip 22 by a wire 35c. The ground surface 34 of the high-frequency wiring board 30 is connected to the comb-shaped ground electrode 24 of the laser array chip 22 by wires 35a and 35b. The comb-shaped ground electrode 24 of the laser array chip 22 is further connected to a ground surface 37 formed on the subcarrier 21 by wires 38a and 38b. That is, one or more ground electrodes, each of which is disposed at least partially between two adjacent optical functional elements (laser elements), and directly with at least one of the semiconductor substrate and the lower cladding layer. One or more ground electrodes (comb-type ground electrodes) that are in contact and electrically connected are provided. A ground surface is formed on the lower surface (back surface) of the subcarrier 21, and the ground surface 37 on the upper surface and the ground surface on the lower surface are electrically connected.

  The difference from the laser array light source of the prior art is that a comb-shaped ground electrode 24 unique to the present invention exists. That is, in addition to the ends of the high-frequency signal lines of the laser electrode 23 and the high-frequency wiring board 30 being connected by wires, the comb-shaped ground electrode 24 and the ground electrode 37 on the subcarrier 21 are connected by wires. Since the gold wire used in these connections is very short, the resistance of the gold wire is almost negligible. The comb-shaped ground electrode 24 is connected to the lower cladding layer 29 as shown in FIG. Therefore, a wire connection between the comb-shaped ground electrode 24 and the ground electrode 37 can realize a stable low-impedance ground path separately from the ground path from the lower cladding layer 29 to the bottom surface of the laser array chip 22. It becomes. Due to the new ground path between the comb-shaped ground electrode 24 and the ground electrode 37 on the subcarrier 21, the potential of the lower cladding layer 29 shown in FIG. 4B can also be set to a stable ground level. This stabilized ground for the individual channel laser device makes it possible to suppress crosstalk between the channels.

  In the configuration of the conventional laser array light source, as shown in FIG. 2B, a current flows through each signal line wire of the adjacent channel, so a magnetic field is generated so as to surround each wire. To do. Therefore, adjacent signal wires are affected by this magnetic field, causing coupling between the signal wires and crosstalk.

On the other hand, in the configuration of the laser array light source of the present invention, as shown in FIG. 5B, between the signal line wires of adjacent channels, the comb-shaped ground electrode 24 and the ground electrode 37 And a ground wire connection between the comb-shaped ground electrode 24 and the ground surface 34 . These ground connections constitute a stable ground with low impedance. As a result, an effect of electrostatic shielding between the two channels can be obtained, and crosstalk between the channels can be suppressed.
FIG. 7 is a diagram illustrating a result of simulating a difference in crosstalk between channels due to the presence or absence of a ground wire between signal lines of each channel. In the model used for comparison, the distance between the signal line wires is 500 μm, the distance between the signal line wires and the ground wire is 250 μm, each wire diameter is 25 μm, and the length of the aerial wiring portion of the signal line wire and the ground wire is It was 490 μm. In FIG. 7, the vertical axis indicates the amount of attenuation (coupling amount) from one channel to one adjacent channel in dB, and the horizontal axis indicates the signal frequency (GHz). It can be seen that the presence of the ground wire has an effect of suppressing the crosstalk by about 10 dB at the maximum as compared with the case where the ground wire is not present.

  The present invention forms a ground electrode formed so as to surround and separate each laser device of a laser array light source, and the ground electrode is electrically connected to the ground of one or more substrates constituting the laser array light source. A characteristic is that a new ground path is formed in the laser device of each channel by forming the connection. Hereinafter, more specific examples will be described in detail.

First, an embodiment of the laser array light source of the present invention using a direct modulation DFB laser array will be described. This embodiment is an exemplary form showing the effect of the present invention, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.
The laser array light source of the present embodiment is a direct modulation DFB laser array light source having the same configuration as that already shown in FIG. As shown in FIG. 5A, the laser array chip in this embodiment has a configuration of a 4-channel direct modulation DFB laser array in which a multiplexer is integrated on the same substrate. In this embodiment, the repetition distance between channels of each laser device is 400 μm, and a multimode interference type multiplexer (hereinafter referred to as an MMI coupler) is used as a multiplexer.

  In this embodiment, the bias current of each laser is 50 mA, and the signal amplitude of the modulation signal is 40 mAp-p. The laser wavelength was set to 1295 nm, 1300 nm, 1305 nm, and 1310 nm from the short wavelength side, and channel 1, channel 2, channel 3, and channel 4 from the shortest wavelength. On the laser array chip 22 in FIG. 5A, the channel 1, the channel 2, the channel 3, and the channel 4 are sequentially formed from the upper laser device.

  As described above, the potential of the lower cladding layer of each laser device can be stabilized by providing the comb-shaped ground electrode unique to the present invention. It is important to suppress crosstalk between channels that the potential of the lower cladding layer immediately below the core layer is a stable ground. In the configuration of the conventional laser array light source, the core layer is connected to the stable ground on the lower surface of the laser chip through the n-InP substrate. However, since it is difficult to increase the doping concentration on the substrate, the n-InP substrate has a resistance that cannot be ignored.

  In the configuration of the laser array light source of the present invention, as shown in FIG. 6B, the bottom surface of the laser chip 22 is connected to the lower cladding layer via the ground electrode 37, the gold wire 38b, and the comb-shaped ground electrode 24. An electrical path is created. A material such as gold or an electrode has a very small resistance as compared with a semiconductor n layer or a p layer. For this reason, the electrical path connecting the upper cladding layer and the stable ground bottom surface is connected by a wire having a negligible low resistance, and the ground potential of the laser device can be stabilized.

  In the present embodiment, the connection is made by a low resistance wire, but the electrical connection means for connecting the ground electrodes of the two substrates is not limited to the wire, and other electrical connection means can be used. For example, it is possible to connect using a conductive material such as silver paste. For example, referring to FIG. 6B, since the ground surface 34 of the high-frequency wiring board 30 is formed up to the end of the wiring board 30, a bridge formed of a conductive paste instead of the wires 35a and 35b. Depending on the structure, it can be connected to the comb-shaped ground electrode 24 of the laser array chip 22. Similarly, since the comb ground electrode 24 of the laser array chip 22 is formed up to the end of the chip, instead of the wires 38a and 38b, the comb ground electrode 24 and the side surface of the chip 22 (with the conductive paste) are used. The metal ground structure that integrally covers the end surface) and the ground surface 37 of the subcarrier 21 can be formed to connect the comb-shaped ground electrode 24 and the ground surface 37.

  The conductive paste is known as, for example, a paste-like material in which low-temperature molten metal particles are dispersed in a thermosetting resin. As an alternative to solder, molten metal particles are self-organized to form metal joints, and the surroundings are reinforced by thermosetting resin, thereby providing connection reliability.

The present invention also has an aspect as an invention of a method for producing a multi-channel laser array light source. That is, a plurality of optical functional elements having a layer structure including at least a semiconductor substrate, a lower cladding layer, a core layer, and an upper cladding layer, which convert an electrical signal into an optical signal, and two adjacent optical functional elements One or more ground electrodes, each of which is at least partially disposed therebetween, and is in direct contact with and electrically connected to at least one of the semiconductor substrate and the lower cladding layer In a method of manufacturing a multi-channel laser array light source including a laser array chip including an electrode, a chip-mounted ground electrode is formed on an upper surface, and a ground electrode electrically connected to the chip-mounted ground electrode is formed on a lower surface Mounting the laser array chip on a subcarrier; and grounding the laser array chip. Connecting the chip-mounted ground electrode on the subcarrier by wire wiring, and mounting a high-frequency wiring board having a plurality of signal wirings and ground electrodes for guiding the electrical signal on the subcarrier. When,
A method for producing a multi-channel laser array light source, comprising: connecting the ground electrode of the high-frequency wiring board and the chip-mounted ground electrode on the subcarrier by wire wiring.

  The mounting process of the laser array light source of the present invention corresponding to the above-described method invention will be described with reference to FIGS. First, the multiplexer-integrated DFB laser array chip 22 is mounted on the subcarrier 21. At this time, the ground electrode 37 formed on the subcarrier 21 and the comb-shaped ground electrode 24 on the laser array chip 22 are connected by gold wires 38a and 38b using wire bonding.

  Next, the wiring support portions 31a and 31b are fixed to both ends of the subcarrier 21, and the high-frequency wiring board 30 is mounted on the wiring support portions 31a and 31b. The wiring support portions 31 a and 31 b form a hollow structure and can electrically connect the subcarrier 21 and the high-frequency wiring board 30.

  Finally, between the end of the signal line 33 on the high-frequency wiring board 30 and the laser electrode 23 on the laser array chip 22, and between the ground electrode 34 on the high-frequency wiring board 30 and the comb-shaped ground on the laser array chip 22. The electrodes 24 are connected by wire bonding technology using gold wires 35a, 35b, and 35c. Next, characteristics of the laser array light source of this embodiment will be described.

  FIG. 8 is a diagram illustrating a measurement system of the BER characteristic of the laser array light source according to the first embodiment. Four BER measurement systems are configured so that the BER can be measured independently for each of the four channel lasers of the laser array light source 50. A DC power supply 13-1, a pulse generator 11-1, and a bias T12-1 are provided for one channel, and a modulation signal is supplied to a signal line having a high frequency wiring board wavelength via a high frequency probe 51a. . The modulated optical output is efficiently coupled by the tip fiber 52 and is received by the optical receiver 15 via the variable wavelength filter 17 and the optical variable attenuator 14. An error is observed by the error detector 16.

FIG. 9 is a diagram showing a BER characteristic measurement system of a laser array light source without a comb-shaped ground electrode and a ground wire manufactured for comparison. The BER characteristics of the DFB laser array light source 60 mounted by the same structure and process as in Example 1 were measured except that there were no comb-shaped ground electrode and ground wire. The measurement conditions in both measurement systems were a signal rate of 10 Gbps, a 31-stage pseudo-random bit sequence (PRBS2 ³¹ -1), and room temperature conditions were kept constant at 25 ° C.

  First, measurement was performed by operating each channel independently. As a result of measuring the laser array light source 50 of this example having a comb-shaped ground electrode, error-free operation was confirmed in all channels. The minimum light sensitivity was -19.5 dBm, -18.5 dBm, -19 dBm, and -18 dBm for channels 1, 2, 3, and 4, respectively. Further, even in the laser array light source 60 having no comb-shaped electrode, error-free operation can be confirmed in all channels, and the minimum light receiving sensitivity is −18.5 dBm, −19 dBm, −18. They were 5 dBm and -18 dBm.

  Next, measurement was performed by operating all channels simultaneously. As a result of measuring the laser array light source 50 of this example having a comb-shaped ground electrode, error-free operation was confirmed in all channels. The minimum photosensitivity was -19 dBm, -18 dBm, -19 dBm, and -17.5 dBm for channels 1, 2, 3, and 4, respectively. In addition, even in the laser array light source 60 without the comb-shaped electrode, error-free operation was confirmed in all channels, but the minimum light receiving sensitivity was −15.5 dBm, −13.5 dBm, The sensitivity deteriorated by 3 to 5 dB as compared with the case of independent operation of one channel, being -14 dBm and -14 dBm.

In the laser array light source 50 having the comb-shaped ground electrode structure, the minimum light receiving sensitivity is hardly deteriorated between the simultaneous operation of all channels and the independent operation of one channel. On the other hand, in the laser array light source 60 without the comb-shaped ground electrode, the minimum light receiving sensitivity is clearly deteriorated in the simultaneous operation of all channels as compared with the independent operation of one channel. This difference is considered to be caused by waveform degradation due to crosstalk between channels.
Next, it was measured how much the oscillation wavelength of channel 2 was shifted in each case of simultaneous operation of all channels and independent operation of one channel. At this time, the measurement was performed under the condition that the laser bias current was 50 mA and no modulation signal was applied. The oscillation wavelength of channel 2 for independent operation of one channel was 1300.1 nm for a light source with a comb-shaped ground electrode and 1299.95 nm for a light source without a comb-shaped ground electrode. Next, the oscillation wavelength of channel 2 when a bias current is applied simultaneously to all channels was 1300.2 nm for a laser array light source with a comb-shaped ground electrode and 1300.3 nm for a laser array light source without a comb-shaped ground electrode. . Since the oscillation wavelength shift is considered to indicate an increase in the active layer temperature, it can be seen that the comb ground electrode of the present invention is effective in suppressing thermal crosstalk between adjacent channels.

  As described above, it is clear that the provision of the comb-shaped ground electrode unique to the multi-channel laser array light source of this embodiment is effective in reducing both electrical crosstalk and thermal crosstalk. is there. In this embodiment, the application example to the direct modulation DFB laser is shown, but the ground electrode of the present invention can be applied to other types of lasers. That is, a ground electrode formed so as to surround and separate each laser device of the laser array light source is formed, and electrical connection to the ground of one or more substrates constituting the laser array light source is made to the ground electrode. By forming, the same effect can be obtained.

  In the present embodiment, the comb-shaped ground electrode in which a part of the ground electrode is arranged between the laser devices of each channel is exemplarily shown. However, electrical or thermal isolation is realized between the laser devices of each channel. If possible, the shape is not limited to a comb shape. Moreover, although the comb-shaped ground electrode of the present embodiment is exemplarily shown as an integrated one having no discontinuous portion, the discontinuous portion of the electrode that is sufficiently shorter than the wavelength (1/4 wavelength) of the electromagnetic wave of the electric signal. Even in the case of a ground electrode having a shape such as a cut line or a gap, electrical or thermal isolation can be realized. That is, as long as the necessary ground wire of the gold wire and the ground electrode are in direct contact with at least one of the semiconductor substrate and the lower clad layer, the present invention is not limited to the comb shape, and the effects of the present invention can be exhibited. In this embodiment, the laser devices for each channel are arranged on a straight line. However, even when the laser devices are arranged on a curved line, a part of the ground electrode is located between the laser devices for each channel. Needless to say, electrical isolation or thermal isolation can be realized.

An embodiment in which the laser array light source of the present invention is applied to an electroabsorption modulator integrated distributed feedback (EADFB) laser will be described. This embodiment is also an exemplary form showing the effects of the present invention, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.
FIG. 10 is a diagram illustrating a configuration of an EADFB laser array chip used in the laser array light source according to the second embodiment of the present invention. FIG. 10A shows the configuration of a multi-channel laser array chip 71 used in this embodiment. FIG. 10B shows a cross section of the YY ′ portion of the chip. As shown in FIG. 10A, the laser array chip 71 includes a two-channel EADFB laser array in which a multiplexer 70 is integrated on the same substrate. The EADFB laser is well known as a light source with a modulation function in which a DFB laser that emits light of constant intensity and an EA modulator that modulates the light intensity are integrated on one chip. If attention is paid to the lower channel of FIG. 10A, the laser of one channel has an EA modulator electrode 73a and a DFB laser electrode 72a. Further, the laser array chip 71 according to the present invention is characterized in that it has a U-shaped ground electrode 74a formed so as to surround the EA modulator electrode 73a and the DFB laser electrode 72a.

  That is, the laser array light source of the present embodiment has two portions of the ground electrode between two adjacent optical functional elements, and the portions on both sides of one optical functional element are the laser array. An integrated ground electrode surrounding the one optical functional element is formed on the chip surface, and the integrated ground electrode of the one optical functional element and the integrated ground electrode of another optical functional element are the laser array. They are not connected on the chip surface and are electrically connected only via the semiconductor substrate or the lower cladding layer. The integral ground electrode includes, for example, a U-shaped ground electrode 74a in the present embodiment.

  The comb-shaped ground electrode 24 in the first embodiment shown in FIG. 4A is formed so as to surround the DFB laser electrodes 23a and 23b, and the comb-shaped ground is formed in a gap portion between adjacent DFB laser electrodes. Electrode 24 was formed. Further, the ground electrode portions of each gap portion are all connected, and the comb-shaped ground electrode 24 is configured as an integrated unit that is entirely connected.

  On the other hand, in the U-shaped ground electrode 74a of this embodiment shown in FIG. 10A, two ground electrodes 74a and 74b are formed in the gap portion between adjacent channels. . That is, a part of the two ground electrodes 74a and 74b between the DFB laser electrode 72a and the DFB laser electrode 72a in FIG. 10A is formed between two adjacent optical function elements in the claims. , Corresponding to two parts of the ground electrode. These ground electrodes are configured separately on at least the surface of the laser array chip 71. That is, the U-shaped ground electrode surrounding the laser device of one channel is connected to the ground electrodes on both sides of the DFB laser electrode of the channel to form a U-shaped pattern. This corresponds to forming an integral ground electrode surrounding one optical functional element on the laser array chip surface in the claims. The U-shaped ground electrodes are connected to each other by the substrate of the laser array chip 71. In the claims, the integrated ground electrode of one optical functional element and the integrated ground electrode of another optical functional element are not connected on the laser array chip surface, and the semiconductor substrate or the lower portion This corresponds to electrical connection only through the cladding layer.

Referring to the cross-sectional view of the YY ′ portion in FIG. 10B, the core layer 76 is formed on the semiconductor substrate (lower clad layer) 75, and the upper clad layers 77a and 77b are further formed. ing. The upper cladding layers 77a and 77b of each channel are separated by dielectric insulating films 78a and 78b, and a device that actually functions as an EA modulator is formed. Two EA modulator electrodes 73a and 73b are formed thereon. The U-shaped ground electrodes 74a and 74b are formed so as to surround the EA modulator electrodes 73a and 73b, respectively. The U-shaped ground electrodes 74 a and 74 b are connected via a substrate 75. The U-shaped ground electrodes 74a and 74b are formed of insulating films (for example, SiO ² ) 79a, so that the upper cladding layers 77a and 77b do not short-circuit with the lower cladding layer (substrate) 75 and the core layer 76 of the active layer. 79b is formed. The two ground electrodes, the U-shaped ground electrode 74 a and the U-shaped ground electrode 74 b, are electrically connected only by the lower clad layer (substrate) 75. That is, it should be noted that the two U-shaped ground electrodes 74a and 74b are not connected to each other as electrode patterns on the laser array chip surface.

  In this embodiment, the repetition distance of each laser channel is set to 500 μm, and a multimode interference type multiplexer (MMI coupler) is used as a multiplexer. As the ground electrode formed on the laser array chip 71, a U-shaped ground electrode independent for each channel was used as described above. As described above, the electrode pattern on the surface of the laser array chip 71 has a ground electrode structure separated between channels so that the fluctuation of the ground potential caused by the operation of one channel is not transmitted to the ground electrode of the adjacent channel. Has the effect of

  The oscillation wavelengths of the laser of this example were 1550 nm and 1560 nm from the short wavelength side, and channels 1 and 2 were set from the shortest wavelength. On the laser array chip 71, the channels 1 and 2 correspond in order from the upper laser device. The bias current of the DFB laser was 80 mA, and the bias voltage of the EA modulator was -1.5V for channel 1 and -1.6V for channel 2.

  FIG. 11 is a diagram showing a configuration of a laser array light source of Example 2 using an EADFB laser array chip. U-shaped ground electrodes 74a and 74b formed so as to surround and separate each laser device on the laser array chip 71 are formed, and a laser array light source is configured with respect to the U-shaped ground electrodes. By forming a wire connection to the ground of the other substrate (subcarrier 80, high-frequency wiring boards 81a and 81b), a new ground path of the laser device of each channel is formed. Reduction of electrical crosstalk between channels and thermal crosstalk is based on the same operation principle as described in the first embodiment.

  Furthermore, in this embodiment, since a U-shaped structure in which the ground electrode is separated for each channel is used, it is possible to prevent the fluctuation of the ground potential due to the operation of one channel from being transmitted to the ground electrode of the adjacent channel. Thus, further crosstalk suppression can be achieved. Further, in this embodiment, the hollow structure using the support members 31a and 31b as in the first embodiment shown in FIG. 5 is not used, and the laser array chip 71 and the high-frequency wiring board 81a on the subcarrier 80, 81b is directly mounted and arranged so that the circuit configuration surfaces are substantially the same height. Wire connection between the U-shaped ground electrodes 74a and 74b and the ground surface of another substrate will be described later. A ground surface is formed on the lower surface (back surface) of the subcarrier 80, and the ground surface 86 on the upper surface and the ground surface on the lower surface are electrically connected.

  In FIG. 11, the connection place between the grounds by the wire in a present Example is not restricted only to each position shown by FIG. The number of wires is not limited to that shown in FIG. Also in this embodiment, the grounds of the two substrates are connected by a low resistance wire, but the electrical connection means for connecting the ground electrodes of the two substrates is not limited to the wires, but other electrical connections. Means are available. As described in Embodiment 1, it is possible to connect using a conductive material such as silver paste. For example, the U-shaped ground electrode 24, the side surface of the laser array chip 71, and the ground of the subcarrier 80 are formed by conductive paste from the U-shaped ground electrodes 74 a and 74 b to the ground surface 86 of the subcarrier 80. A U-shaped ground electrode 24 and the ground surface 86 can be connected by forming a metal joint structure that covers the surface 86.

  Next, the mounting process of the laser array light source of the present embodiment will be described with reference to FIG. First, the EADFB laser array chip 71 is mounted on the ground electrode 86 on the subcarrier 80. At this time, the U-shaped ground electrodes 74a and 74b are connected to the ground electrode 86 on the subcarrier 80 by a gold wire. The DFB laser electrode 72a is connected to a DC wiring 83a formed on the subcarrier 80 by a gold wire. That is, the method of the present invention further includes a step of connecting the DC wiring formed on the subcarrier and the semiconductor distributed feedback laser (DFB laser) electrode on the laser array chip by wire wiring. .

Next, high frequency wiring boards 81 a and 81 b are mounted on the subcarrier 80. In this embodiment, since the laser array light source is composed of two-channel laser devices, two separate high-frequency wiring boards are used. However, the number of high-frequency wiring boards is not limited to this. On the high-frequency wiring board 81a, the signal line 85 a, the terminating resistor 82a is configured,: both sides of the signal line 85 a has a ground surface. The shape and number of high-frequency wiring boards can be changed according to the mounting status of the laser array light source. Finally, the high frequency circuit board 81a, and the end of the signal line 85 a, 85 b of 81b, EA modulator electrode 73a on the laser array chip 71, and 73b, connected by a gold wire. Further, the ground electrodes of the high-frequency wiring boards 81a and 81b and the U-shaped ground electrodes 74a and 74b on the laser array chip 71 are similarly connected with a gold wire using a wire bonding technique.
FIG. 12 is a diagram illustrating a measurement system for the BER characteristics of the laser array light source according to the second embodiment. Two BER measurement systems are configured so that the BER can be measured independently for each of the lasers of the two channels of the laser array light source 90. A DC power supply 13-1, a pulse generator 11-1, and a bias T12-1 are provided for one channel, and a modulation signal is supplied to a signal line having a high frequency wiring board wavelength via a high frequency probe 51a. . DC power supplies 13-3 and 13-4 supply current to the DFB laser. The modulated optical output is efficiently coupled by the tip fiber 92 and received by the optical receiver 15 via the variable wavelength filter 18 and the optical variable attenuator 14. An error is observed by the error detector 16.

  FIG. 13 is a diagram showing a configuration of a BER characteristic measurement system of a laser array light source without a U-shaped electrode and a ground wire manufactured for comparison. The BER characteristics of the DFB laser array light source 100 mounted by the same structure and process as in Example 2 were measured except that there was no U-shaped ground electrode and no ground wire.

The measurement conditions in both measurement systems were a signal rate of 25 Gbps, a 31-stage pseudo random bit sequence (PRBS2 ³¹ -1), a signal amplitude voltage of 2.0 Vpp, a crosspoint of 70%, and a room temperature condition of 25 ° C. The measurement was performed.

  First, measurement was performed by operating each channel independently. As a result of measuring the laser array light source of this example having a U-shaped ground electrode, error-free operation was confirmed in all channels. The minimum light receiving sensitivity was -14.5 dBm and -14 dBm for channels 1 and 2, respectively. Further, even in a light source without a U-shaped electrode, error-free operation was confirmed in all channels, and the minimum light receiving sensitivity was -14.5 dBm and -14 dBm for channels 1 and 2, respectively.

  Next, measurement was performed by operating two channels simultaneously. As a result of measuring the laser array light source 90 of this example having a U-shaped ground electrode, error-free operation was confirmed in all channels. The minimum light receiving sensitivity of channels 1 and 2 was -14 dBm and -14 dBm, respectively. Further, even in the laser array light source 100 having no U-shaped electrode, error-free operation was confirmed in all channels, but the minimum light receiving sensitivities were -12.5 dBm and -12.5 dBm in channels 1 and 2, respectively. The light receiving sensitivity was deteriorated by nearly 2 dB as compared with the channel independent operation.

In the laser array light source 90 having the U-shaped ground electrode structure, the minimum light receiving sensitivity is hardly deteriorated in the case of the two-channel simultaneous operation and the one-channel independent operation. On the other hand, in the laser array light source 100 without the U-shaped ground electrode, the minimum light receiving sensitivity is clearly deteriorated in the simultaneous operation of two channels as compared with the independent operation of one channel. This difference is considered to be caused by waveform degradation due to crosstalk between channels.
Next, it was measured how much the oscillation wavelength of channel 2 was shifted between simultaneous operation of all channels and independent operation of one channel. At this time, the measurement was performed under the condition that the laser bias current was 80 mA and no modulation signal was applied. The oscillation wavelength of channel 2 for independent operation of one channel was 1560.5 nm for a light source with a U-shaped ground electrode and 1560.05 nm for a light source without a U-shaped ground electrode. Next, the oscillation wavelength of channel 2 when a bias current is simultaneously applied to all channels is 1560.52 nm for a laser array light source with a U-shaped ground electrode and 1560 .5 for a laser array light source without a U-shaped ground electrode. It was 52 nm. Since the shift in the oscillation wavelength is considered to indicate an increase in the temperature of the active layer, the U-shaped ground electrode in this example is similar to the comb-type ground electrode in Example 1 in terms of thermal crosstalk between adjacent channels. It turns out that it is effective in suppression of this.

  In this embodiment, the U-shaped ground electrode in which two portions of the ground electrode are arranged between the laser devices of the respective channels is exemplarily shown. However, an electrical or thermal isolation is provided between the laser devices of the respective channels. However, the shape is not limited to a U shape. In addition, the U-shaped ground electrode of the present embodiment is shown as an example of an integrated one having no discontinuous portion, but the electrode having an electrode sufficiently shorter than the wavelength (1/4 wavelength) of the electromagnetic wave of the electrical signal is not shown. Even in the case of a ground electrode having a shape such as a continuous portion, a cut, or a gap, electrical isolation and thermal isolation can be realized. That is, the necessary electrical connection (for example, gold wire ground wiring) is made to the subcarrier and the high-frequency wiring board, and the ground electrode of the laser array chip is in direct contact with at least one of the semiconductor substrate and the lower cladding layer. For example, the present invention is not limited to a U-shape, and the effects of the present invention can be exhibited. In this embodiment, the laser devices for each channel are arranged on a straight line. However, even if the laser devices are arranged on a gentle curve, a part of the ground electrode is placed between the laser devices for each channel. It goes without saying that electrical isolation and thermal isolation can be realized as long as there is.

  The Example which comprised the laser array light source of this invention on the semi-insulating board | substrate is shown. The configuration of the present embodiment is similar to the U-shaped ground electrode of the second embodiment in the shape of the ground electrode formed between the channels of the laser device, but the direct modulation DFB laser array chip similar to the first embodiment. Is used. This is different from the first embodiment in the configuration of the lower cladding layer of the laser device and the configuration of the optical multiplexer. This embodiment is also an exemplary form showing the effects of the present invention, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

  FIG. 14 is a diagram showing a configuration of a direct modulation DFB laser array chip used in the laser array light source according to the third embodiment of the present invention. FIG. 14A shows the configuration of a multi-channel laser array chip 110 used in this embodiment. FIG. 14B shows a cross section of the XX ′ portion of the chip. As shown in FIG. 14A, in the laser array chip 110, the multiplexer is not integrated on the chip. Further, since direct modulation is performed in the laser array chip 110 in the present invention, only the DFB laser electrodes 112a and 112b are formed as the laser device as in the configuration of the first embodiment. On the other hand, the ground electrode formed between the channels is provided with U-shaped ground electrodes 111a and 111b formed so as to surround the DFB laser electrodes 112a and 112b as in the second embodiment. is there.

  In the U-shaped ground electrode of the present embodiment shown in FIG. 14A, two ground electrodes 111a and 111b are formed between gaps between adjacent channels, for example, between DFB laser electrodes 112a and 112b. Has been. These ground electrodes are configured as separate and independent elements at least on the surface of the laser array chip 100. That is, the U-shaped ground electrode surrounding the laser device of one channel is connected to the ground electrode portions on both sides of the DFB laser electrode of the channel to form a U-shaped pattern. That is, different U-shaped ground electrodes for different channels are connected by the low resistivity layer 114 formed on the laser array chip 110 unique to this embodiment.

  Referring to the cross-sectional view taken along the line XX ′ in FIG. 14B, the laser array chip 100 of the present embodiment has a low resistivity n-InGaAsP layer 114 formed on a semi-insulating InP substrate 113. ing. On the low resistivity n-InGaAsP layer 114, an n-InP lower cladding layer 115, a core layer 118, and a p-InP upper cladding layer 117 are sequentially formed. Both sides of the core layer 118 and the upper cladding layer 117 are separated by semi-insulating InP layers 116a and 116b. U-shaped ground electrodes 111a, 111b, and 111c are formed so as to surround each laser device. In this embodiment, the U-shaped ground electrodes 111 a, 111 b, and 111 c are connected not to the n-InP lower cladding layer 115 but to the low resistivity n-InGaAsP layer 114. That is, the layer structure of the laser device described above includes a low resistivity layer 114 disposed immediately below the lower cladding layer 115 and having a resistivity lower than that of the lower cladding layer 115, and the U-shaped ground electrodes 111a and 111b. 111c are in contact with the low resistivity layer 114.

  By connecting the U-shaped ground electrode to the n-InGaAsP layer 114 having a lower resistivity than the n-InP lower cladding layer 115, the lower cladding layer 115 is connected to the subcarrier on which the laser array chip 100 is mounted. It is characterized by a structure that further lowers the impedance of the electrical path to the ground electrode.

  In this example, the repetition distance of the channel of each laser device was 400 μm. The laser bias current was 50 mA, and the signal amplitude of the modulation signal was 40 mApp. The oscillation wavelength of the laser was 1295 nm, 1300 nm, 1305 nm, and 1310 nm from the short wavelength side, and channels 1, 2, 3, and 4 were set from the shortest wavelength. The laser array chip corresponds to channels 1, 2, 3, and 4 in order from the top of FIG.

  FIG. 15 is a diagram showing a configuration of a laser array light source of Example 3 using a direct modulation DFB laser array chip. In this embodiment, the multiplexer is not integrated on the laser array chip, but is configured as a planar lightwave circuit (quartz PLC 126) made of quartz. Optical coupling from the laser array chip 110 to the planar lightwave circuit 126 is performed by the lens array 125. A U-shaped ground electrode formed so as to surround and separate each laser device on the laser array chip 110 is formed, and one or more other elements constituting the laser array light source are formed with respect to the U-shaped ground electrode. By forming a wire connection to the ground of the substrate (subcarrier 121, high frequency wiring board 122), a new ground path of the laser device of each channel is formed. Reduction of electrical crosstalk between channels and thermal crosstalk is realized based on the same operation principle as described in the first embodiment. In the present embodiment, a U-shaped ground electrode in which the ground electrode is separated for each channel is used as in the second embodiment, and further connected to the n-InGaAsP layer 114 having a low resistivity. Thereby, the impedance of the electrical path from the lower clad layer 115 to the ground electrode on the subcarrier on which the laser array chip 100 is mounted can be further reduced. It is possible to prevent the fluctuation of the ground potential due to the operation of one channel from being transmitted to the ground electrode of the adjacent channel, and it is possible to further suppress the crosstalk than in the first and second embodiments.

  FIG. 16 is a diagram showing a configuration of a laser array light source according to the third embodiment of the present invention viewed from the side. This embodiment does not have a hollow structure using the support members 31a and 31b as in the first embodiment shown in FIG. 5, and the laser array chip 110 and the high-frequency wiring board 122 are directly mounted on the subcarrier 121. The circuit configuration surfaces are arranged so as to have substantially the same height. The high frequency wiring board 122 is provided with a signal line 123 and a termination resistor 128. The hatched areas on both sides of the signal line are ground electrodes. Wire connection between the U-shaped ground electrode and the ground electrode of another substrate will be described later.

  Here, the mounting process of the laser array light source of the present embodiment will be described with reference to FIGS. First, the DFB laser array chip 110 is mounted on the ground electrode 124 on the subcarrier 121. At this time, the U-shaped ground electrode is connected to the ground electrode 124 on the subcarrier 121 by a gold wire.

  Next, five high-frequency wiring boards 122 are mounted on the subcarrier 121. Then, the signal line 123 of the high-frequency wiring board 122 and the DFB laser electrode 112 of the laser array chip 110 are connected by a gold wire. Further, the ground electrode on both sides of the signal line of the high-frequency wiring board 122 and the U-shaped ground electrode of the laser array chip 110 are connected by a gold wire. Finally, the lens array 125 and the optical multiplexer 126 are aligned and mounted so that the light from each channel of the DFB laser is coupled to the optical multiplexer 126 at the maximum.

  In FIG. 15, the connection place between the grounds by the wire in a present Example is not restricted only to each position shown by FIG. Further, the number of wires is not limited to that shown in FIG. Further, as described in the first and second embodiments, electrical connection means other than the wires can be used for at least a part of the wires. For example, the U-shaped ground electrode and the ground surface 124 of the subcarrier 121 are covered with a metal paste structure that covers the U-shaped ground electrode, the side surface of the laser array chip 110, and the ground surface 124 of the subcarrier 121 with a conductive paste. The U-shaped ground electrode 24 and the ground surface 124 can be connected.

  FIG. 17 is a diagram illustrating a measurement system for the BER characteristics of the laser array light source according to the third embodiment. Four BER measurement systems are configured so that the BER can be measured independently for each of the four channel lasers of the laser array light source 140. A DC power supply 13-1, a pulse generator 11-1, and a bias T12-1 are provided for one channel, and a modulation signal is supplied to the signal line of the high frequency wiring board 122 via the high frequency probe 141a. . The modulated optical output is efficiently coupled by the tip fiber 142 and is received by the optical receiver 15 via the variable wavelength filter 17 and the optical variable attenuator 14. An error is observed by the error detector 16.

FIG. 18 is a diagram illustrating a configuration of a BER characteristic measurement system of a laser array light source 150 that is prepared for comparison and does not have a wire connecting a U-shaped ground electrode and a high-frequency wiring board ground. The BER characteristics of the DFB laser array light source 150 mounted by the same structure and process as in Example 3 were measured except that there was no wire connecting the U-shaped ground electrode and the high-frequency wiring board ground. The measurement conditions in both measurement systems were a signal rate of 10 Gbps, a 31-stage pseudo random bit sequence (PRBS 2 ³¹ -1), and room temperature conditions at a constant 25 ° C.

  First, measurement was performed by operating each channel independently. As a result of measuring the laser array light source 140 of the present example having a wire connection between the ground electrode of the high-frequency wiring board 122 and the U-shaped ground electrode, an error-free operation was confirmed in all channels. The minimum light sensitivity was -18 dBm, -18.5 dBm, -18.5 dBm, and -18 dBm for channels 1, 2, 3, and 4, respectively. Further, even in the laser array light source 150 having no wire connection between the ground electrode of the high-frequency wiring board 122 and the U-shaped ground electrode, an error-free operation can be confirmed in all channels, and the minimum light receiving sensitivity is the channel 1, 2, 3 4 were -19 dBm, -19 dBm, -18.5 dBm, and -18 dBm, respectively.

  Next, measurement was performed by simultaneously operating four channels. As a result of measuring the laser array light source 140 of the present example having a wire connection between the ground electrode of the high-frequency wiring board 122 and the U-shaped ground electrode, an error-free operation was confirmed in all channels. The minimum photosensitivity was -18 dBm, -18 dBm, -18.5 dBm, and -17.5 dBm for channels 1, 2, 3, and 4, respectively. Further, even in the laser array light source 150 having no wire connection between the ground electrode of the frequency wiring board 122 and the U-shaped ground electrode, an error-free operation could be confirmed in all channels. -17.5 dBm, -17 dBm, -15.5 dBm, and -16.5 dBm, respectively, and the deterioration of the light receiving sensitivity was observed in the range of about 2 to 3 dB compared to the case of the single channel independent operation.

In the laser array light source 140 that has a wire connection between the ground electrode of the high-frequency wiring board 122 and the U-shaped ground electrode, the minimum light receiving sensitivity is almost lower in the simultaneous operation of four channels than in the independent operation of one channel. Does not deteriorate. On the other hand, in the laser array light source 150 having no wire connection between the ground electrode of the high-frequency wiring board 122 and the U-shaped ground electrode, it is clearly the minimum in the simultaneous operation of four channels compared to the independent operation of one channel. Photosensitivity deteriorated. This difference is considered to be caused by waveform degradation due to crosstalk between channels.
However, in the laser array light source without the ground electrode of the first embodiment, the laser array light source without the wire connection of this embodiment is compared with the degree of deterioration of the minimum light receiving sensitivity between the simultaneous operation of four channels and the independent operation of one channel. The degree of deterioration of the minimum light receiving sensitivity is small. This is considered to be due to the effect that the ground potential of the lower cladding layer is further stabilized by the U-shaped ground electrode between the electrode pads of the DFB laser.

  It is apparent that the U-shaped ground electrode used in the multi-channel laser array light source of this embodiment is effective in reducing crosstalk between channels of the laser device. As described above, according to the present invention, it is possible to perform stable operation by suppressing signal deterioration due to crosstalk between channels and ensuring thermal isolation between adjacent channels to suppress a shift in laser oscillation wavelength. A multi-channel laser array light source can be realized.

  The present invention can be used in an optical communication system. In particular, it can be used as a light source for an optical communication system.

1, 21, 80 Subcarrier 2, 22, 71, 103, 110 Laser array chip 3, 104 Wire 4, 23, 112a, 112b DFB laser electrode 5, 30, 81a, 81b, 105 High frequency wiring board 6a, 6b, 31a , 31b Support portion 7, 32, 82a, 82b, 106, 128 Termination resistor 24 Comb-shaped ground electrode 26, 78 Dielectric insulating film 27, 117 Upper cladding layer 28, 76, 118 Core layer 29, 75, 115 Lower cladding layer 33, 85a, 85b High-frequency wiring 37, 86, 124 Ground plane 74a, 74b, 111a, 111b, 111c U-shaped ground electrode 113 Substrate 114 Low resistivity layer 116a, 116b Semi-insulating InP layer

Claims (8)

A plurality of optical functional elements having a layer structure including at least a semiconductor substrate, a lower cladding layer, a core layer, and an upper cladding layer, and converting an electrical signal into an optical signal;
One or more ground electrodes, each of which is at least partially disposed between two adjacent two of the plurality of optical functional elements, and is in direct contact with at least one of the semiconductor substrate and the lower cladding layer. And a laser array chip including one or more ground electrodes connected to each other ,
The two portions of the ground electrode are provided between two adjacent ones of the plurality of optical functional elements, and the portions on both sides of one optical functional element are arranged on the surface of the laser array chip. An integral ground electrode surrounding the functional element is configured, and the integral ground electrode of the one optical functional element and the integral ground electrode of the other optical functional element are not connected on the laser array chip surface. First, the multi-channel laser array light source is electrically connected only through the semiconductor substrate or the lower cladding layer . A plurality of optical functional elements having a layer structure including at least a semiconductor substrate, a lower cladding layer, a core layer, and an upper cladding layer, and converting an electrical signal into an optical signal;
A comb-shaped ground electrode having at least a part thereof disposed between two adjacent two of the plurality of optical functional elements, and is in direct contact with and electrically connected to at least one of the semiconductor substrate and the lower cladding layer. Comb-shaped ground electrode and
A laser array chip including:
A chip-mounted ground electrode is formed on the upper surface, a ground electrode electrically connected to the chip-mounted ground electrode is formed on the lower surface, and a subcarrier in which the laser array chip is disposed on the chip-mounted ground electrode;
A high-frequency wiring board having a plurality of signal wirings and a ground electrode for guiding the electrical signal;
Electrical connection means (wire) for directly connecting between the comb-shaped ground electrode of the laser array chip and at least one of the chip-mounted ground electrode of the subcarrier or the ground electrode of the high-frequency wiring board
Multi-channel laser array light source, characterized in that it comprises a. A chip-mounted ground electrode is formed on the upper surface, a ground electrode electrically connected to the chip-mounted ground electrode is formed on the lower surface, and a subcarrier in which the laser array chip is disposed on the chip-mounted ground electrode;
A high-frequency wiring board having a plurality of signal wirings and a ground electrode for guiding the electrical signal;
The multi-channel laser array light source according to claim 1 , further comprising: electrical connection means for connecting the laser array chip, the subcarrier, and the high-frequency wiring board. And the chip mounting ground electrode of the sub-carrier, between the ground electrode of the laser array chip is at least one place or more, claim 2, characterized in that it is electrically connected by an electrical connection means Or the multi-channel laser array light source according to 3; Wherein said ground electrode on the high frequency circuit board, between the ground electrode of the laser array chip, the electrical connection means according to claim 2 or 3, characterized in that it is electrically connected to the multi Channel laser array light source.   The layer structure includes a low resistivity layer disposed immediately below the lower cladding layer and having a resistivity lower than that of the semiconductor substrate, and the ground electrode is in contact with the low resistivity layer. The multi-channel laser array light source according to claim 1.   6. The multi-channel according to claim 1, wherein an optical multiplexer that multiplexes optical signals output from the respective optical functional elements into one optical path is formed on the laser array chip. Laser array light source.   6. The optical functional element according to claim 1, wherein the optical functional element comprises a semiconductor distributed feedback laser (DFB laser), or a DFB laser and an electroabsorption optical modulator (EA modulator). Channel laser array light source.

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