JP2001281478A - Optical integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that crosstalk noises from a light emitting element easily flow to a light receiving element via a heat radiating plate and receiving performance of the light receiving element is largely restricted when the light emitting element and the light receiving element of the optical integrated circuit are simultaneously operated, with respect to mounting structure of the optical integrated circuit wherein electric crosstalk noises via the heat radiating plate between the light emitting element and the light receiving element of the optical integrated circuit are reduced. SOLUTION: In the optical integrated circuit wherein the light emitting element and the light receiving element are mounted on the insulation layer of the upper surface of the substrate, a metallic plate which covers the rear surface of the substrate and is shaped so that the rear surface of the substrate in the vicinity of the backside of the mounted light receiving element is exposed, is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION An optical integrated circuit according to the present invention comprises an ATM-PON (Asynchronous Transfer Mode-Pass) for simultaneous transmission and reception.
Wavelength division multiplexing using light of different wavelengths for transmission and reception as optical communication for (ive Optical Network): Wavelength Divisi
On multiplexing (hereinafter WDM) transmission or space division multiplexing (hereinafter SDM) transmission using a two-core fiber and using each fiber exclusively for transmission or reception is used. The present invention relates to a structure for suppressing the propagation of electrical crosstalk noise from a transmitting section having a light emitting element to a receiving section having a light receiving element in an optical integrated circuit. In recent years, with the explosive demand for data communication represented by the Internet and the like, cost reduction and further improvement of transmission efficiency are required for large-capacity optical communication. In optical integrated circuits, multiple optical devices are mounted on a common substrate (platform) as a bare chip, so that the number of housing components for each device can be reduced, and it is attracting attention as an effective method of reducing costs. Also,
In order to improve transmission efficiency, the conventional transmission / reception time division method TDM
(Time Division Multiplexing) or TCM (Time Compress
It is promising that the transition from ion multiplexing to simultaneous transmission and reception using WDM, SDM, etc. To realize such simultaneous transmission and reception in an optical integrated circuit, in order to secure the minimum receiving sensitivity of the receiver,
It is important to suppress electrical crosstalk (transmission signal and noise accompanying the transmission signal) from the transmission unit that drives the light emitting element to the reception unit that has the light receiving element.

[0002]

2. Description of the Related Art FIG. 8 shows a mounting structure of a conventional optical integrated circuit used for TDM transmission. In a conventional mounting structure of an optical integrated circuit, a transmitting electrode 3 and a receiving electrode 4 are formed on the same substrate 2 having an electric insulating layer 1 (used as an optical waveguide layer), and a light emitting element 5 and a light emitting element 5 are formed on the respective electrodes. Light receiving element 6
Is installed. Each electrode is connected to an external device (printed circuit board, LSI
) And the bonding wires 7. Further, the entire optical integrated circuit in which the light emitting element 5 and the light receiving element 6 are hybrid-mounted on the same common substrate via an electrical insulating layer is dissipated by a lead frame (or a Peltier element) or the like (often made of metal). It is mounted on the board 8. The necessity of a heat dissipation structure such as the heat dissipation plate 8 as a conventional optical integrated circuit will be described below.

A light emitting element 5 used in an optical integrated circuit generates heat when emitting light due to the internal resistance of the light emitting element (LD). Further, in general, the higher the temperature is, the more the current required for light emission increases, making it difficult to emit light. Therefore, the operating temperature range is limited.

Therefore, when the light emitting element 5 is mounted on an optical module, a metal heat sink (lead) must be mounted on the mounting structure of the optical integrated circuit board on which the light emitting element 5 is mounted in order to satisfy the operating temperature range. It is necessary to provide a heat dissipation structure such as mounting on a frame) or a temperature control element (made of metal) using the Peltier effect.

[0005] In a small optical transmitting and receiving device in which a light emitting element and a light receiving element are hybrid-mounted on the same substrate,
While a current of several tens of mA flows to drive the light emitting element which is a transmitting unit, a small current of the order of μA or less flows in the receiving unit. For this reason, in order not to affect the receiving performance in the receiving unit, it is required that the current flowing in the receiving unit due to crosstalk from the transmitting unit is in the order of 10 nA to 100 nA.

FIG. 9 is a diagram for explaining a transmission / reception electric crosstalk propagation path in a conventional integrated transmission / reception hybrid optical integrated circuit.

[0007] In the figure, only the minimum necessary components are shown for simplification of the description. In an optical transmitting and receiving device in which a light emitting element (laser diode: LD) 5 and a light receiving element (photo diode: PD) 6 are mounted in a hybrid manner, an optical waveguide layer (oxide film (S
iO2)) 1, and electrodes 3 and 4 are formed thereon. The light emitting element 5 and the light receiving element 6 are mounted on the electrodes 3 and 4, respectively. A heat sink for grounding the back surface of the common substrate 2 is attached.

In an optical integrated circuit in which a light emitting element 5 as a transmitting section and a light receiving element 6 as a receiving section are present on the same substrate 2, crosstalk noise generated by operating the light emitting element 5 propagates to the receiving element 6. I do. There are three possible noise propagation paths. First, as the first route,
There is a path through which crosstalk noise flows from the light emitting element 5 to the light receiving element 6 via the floating capacitance 9 in the air. As a second path, from the light emitting element 5 to the lower part of the transmission unit to the substrate capacitance 11, the substrate resistance 1
4. There is a path through which crosstalk noise flows to the light receiving element 6 via the lower part of the receiving part and the substrate capacitance 11. As a third path, from the light emitting element 5 to the lower part of the transmission unit 11, the substrate resistance 16, the GND common impedance (inductance 17), the substrate resistance 15, the lower part of the substrate capacitance 10 [or the lower part of the transmission unit 13 and the GN
This is a path through which crosstalk noise flows to the light receiving element 6 via the D common impedance (inductance 17) and the lower portion of the receiving section versus the heat sink plate 12].

[0009] As the required signal transmission speed further increases, the propagation amounts of electrical crosstalk noise in the first, second, and third paths in the optical integrated circuit mounting are reduced by the first path <
The second path ≦ the third path. This means that in the first path, the amount of electrical crosstalk noise increases with a first-order slope in the frequency characteristic. In the third path, the amount of electric crosstalk increases with a second-order or higher gradient.
In the comparison between the second path and the third path, the parasitic element 17 of GND becomes high impedance as the frequency increases, so that it is difficult for the crosstalk noise to escape to GND. This increasing trend in frequency is associated with an increase in signal transmission speed.
Further, when the distance between the light emitting element and the light receiving element is longer than the thickness of the common substrate 2, the substrate resistance 15 + the substrate resistance 16 <the substrate resistance 14
This is because the third path has a lower impedance between the light emitting element and the light receiving element than the second path.

That is, the third path having a lower impedance than the second path makes it easier for noise to flow to the light receiving element.

Therefore, in the application to the simultaneous transmission and reception operation of the optical integrated circuit, there is a problem in particular that the influence of the electric crosstalk noise via the heat sink on the receiving unit to the receiving unit.

An object of the present invention is to provide an optical integrated circuit mounting structure for reducing electrical crosstalk noise between a light emitting element and a light receiving element of an optical integrated circuit via a heat sink.

[0013]

According to the present invention, in order to solve the above-mentioned problems, an optical integrated circuit in which a light emitting element and a light receiving element are mounted on an insulating layer on the surface of the substrate is provided. A configuration is provided in which a metal plate having a shape such that the rear surface of the substrate is exposed in the vicinity is provided.

Further, in the optical integrated circuit in which the light emitting element and the light receiving element are mounted on the insulating layer on the surface of the substrate, a metal plate for covering the back surface of the substrate is provided in a plurality. Further, a conductive pattern is formed on the insulating layer on the substrate surface of the optical integrated circuit and between the light emitting element and the light receiving element.

In general, the amount of heat generated by the light receiving element is much smaller than that of the light emitting element, so that a heat radiation structure such as a light emitting element is not required in many cases. In the present invention, utilizing this fact, the heat radiation structure for the light receiving element (receiving unit) is simplified (or deleted) as in the above-described means (shape), and the mounting form is improved.
The propagation of electric crosstalk from the heat radiation structure of the light emitting element to the light receiving element is suppressed.

Further, with respect to the heat radiation property of the light emitting element, since only a part of the heat sink for the light emitting element is deleted, a sufficient heat radiation path can be secured.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a mounting form of an optical integrated circuit and a heat sink for suppressing electric crosstalk between transmission and reception according to the present invention.

As shown in FIG. 1, a radiating plate of a light emitting element which also serves as a mounting surface of an optical integrated circuit in which a light emitting element 5 and a light receiving element 6 are mounted on the same substrate via an electrical insulating layer radiates heat from the light receiving element 6. The distance d1 between the heat radiating plate 18 and the light receiving element 6 such that the distance from the light receiving element 6 and the contact with the heat radiating plate 18 becomes larger than dh around the point where the light is radiated to the plate 18 is determined. The value obtained by subtracting the power of dh to the power of 2 is the radius of the square root of 2, and the shape is obtained by removing the circle centered on the hanging point.

The shape of the heat sink is such that the back surface of the substrate is exposed in the vicinity of the area under the light receiving element.
Further, the heat radiating plates provided on the light emitting element side and the light receiving element side are divided so as not to make electrical contact with each other.

As a result, the specified value (specifying the allowable crosstalk amount) relating to the minimum reception level is satisfied.
By determining the value of dh, it is possible to achieve both the heat dissipation of the light emitting element and the simultaneous operation of transmission and reception, making it possible to apply the hybrid optical integrated circuit to SDM and WDM transmission.

FIG. 2 shows a mounting structure of the hybrid optical integrated circuit according to the first embodiment of the present invention.

The first embodiment shows a hybrid optical integrated circuit in which a light emitting element 5 and a light receiving element 6 are mounted on an electric insulating layer 1 on a common substrate 2.

A radiating plate 18 of the light emitting element also serving as a mounting surface of the hybrid optical integrated circuit is provided with a light emitting device 18 also serving as a mounting surface of the optical integrated circuit in which the light emitting element 5 and the light receiving element 6 are mounted on the same substrate via an electrical insulating layer. The heat sink of the element is a heat sink from the light receiving element 6.
Heat sink 1 such that the distance from the light receiving element 6 to the heat sink 18 is greater than dh around the point of the heat sink 18.
The radius is a value obtained by subtracting the power of dh to the power of 2 from the power of 2 of d1 to the distance dl between the light receiving element 8 and the light receiving element 6, and the radius is the square root of 2; I do.

In FIG. 2, the shape of the heat sink is such that the bottom circle of the triangular pyramid designated by dh, dl and the heat sink is removed from the heat sink.

The specified dl length is equal to the light receiving element 6 and the heat sink 1
When the capacitance 20 and the series resistance 21 of the common substrate 2 are determined between the lower part 8 and the receiver unit 8, the propagation amount of the crosstalk noise that propagates from the light emitting element 5 to the light receiving element 6 via the heat sink 18 is determined. .

Since the allowable crosstalk propagation amount is determined from the specifications of the system in which the hybrid optical integrated circuit is used, the length of dh differs for each system. FIG.
7 shows a mounting structure of a hybrid optical integrated circuit according to a second embodiment of the present invention. The second embodiment shows a hybrid optical integrated circuit in which a light emitting element 5 and a light receiving element 6 are mounted on an electric insulating layer 1 on a common substrate 2.

A radiator plate also serving as a mounting surface of the hybrid optical integrated circuit is separately prepared for the light emitting element 22 and the light receiving element 23, and the light receiving element is centered on the point where the light receiving element 6 hangs down to the heat radiating plate 18. Dh is the distance of the heat sink 18
And the distance dl between the heat sink 18 and the light receiving element 6 is dh <dl
It has a shape such that

Heat sink 23 for light receiving element and heat sink 22 for light emitting element
Is a shape that does not contact at least on the surface on the heat sink side of the hybrid optical integrated circuit. However, since there is parasitic capacitance between the heat sink 23 for the light receiving element and the heat sink 22 for the light emitting element, the heat sink 23 for the light receiving element is made as small as possible and is separated from the heat sink 22 for the light emitting element. It is desirable to install.

FIG. 4 shows a mounting structure of a hybrid optical integrated circuit according to a third embodiment of the present invention. In the third embodiment, the mounting structure of the first embodiment has a rectangular shape, particularly the hybrid optical integrated circuit mounting portion 22 of the heat sink.

FIG. 5 shows a mounting structure of a hybrid optical integrated circuit according to a fourth embodiment of the present invention. In the fourth embodiment, a conductive trap pattern 24 is formed between a light emitting element 5 and a light receiving element 6 on a hybrid optical integrated circuit. However, it is desirable that the position of the conductive trap pattern 24 with respect to the receiving section on which the light receiving element 6 is mounted does not approach the receiving section shortest distance dl of the heat sink 22. In the fourth embodiment, electric crosstalk is transmitted through a heat sink (10, 15, 17, 16, 11 or
In addition to (12, 17, 13), reduction of electrical crosstalk via the stray capacitance 9 between transmission and reception is also performed. Since charges are induced on the conductive trap pattern 22 so as to cancel noise charges generated in the transmission unit due to capacitive coupling between the transmission unit in which the light emitting element 5 is mounted and the trap pattern 24, the reception unit Only the charge that is not canceled is induced, and the electric crosstalk due to the stray capacitance 9 between the transmission and the reception is reduced.

FIG. 6 shows a mounting structure of a hybrid optical integrated circuit according to a fifth embodiment of the present invention. In the fifth embodiment, the trap pattern 24 and the heat sink 22 are electrically connected by wire bonding 25 or the like. By the connection, the heat sink 22 and the trap pattern 24 are electrically in phase,
The crosstalk due to the stray capacitance 9 between the transmission and the reception can be suppressed more than the structure of the embodiment. Further, the first to the first aspects of the present invention
Particularly in the structure of the fifth embodiment, a material having a resistivity of the order of kΩcm or more is used for the common substrate 2. As a result, the resistance 14,15,16 between the transmission and reception via the common substrate 2 becomes a value sufficiently larger than the parasitic resistance (common impedance 17 between transmission and reception) due to the mounting of the heat sink 22, and the electric crosstalk through the substrate and the heat sink. Can be reduced.

FIG. 7 shows a mounting structure of a hybrid optical integrated circuit according to a sixth embodiment of the present invention. In the sixth embodiment of the present invention, the optical waveguides 26, 27, 28 are formed in the electrically insulating layer 1, and the mounting portions 29, 30 for the light emitting elements 5, 6 are connected to the light emitting elements.
5. The light receiving element 6 is recessed from the upper surface of the insulating layer 1 of the hybrid optical integrated circuit so that the light receiving element 6 is optically coupled to the optical waveguides 27 and 28.

Further, in the configuration shown in FIG. 7, in order to cope with a system in which transmission and reception are simultaneously performed using different wavelengths for transmission and reception in one optical waveguide, the transmission section on which the light emitting element 5 is mounted and the light receiving element 6 A dielectric multilayer filter 31 for separating signals having different wavelengths is provided between the receivers on which the is mounted.

In FIG. 7, a signal having a wavelength for reception is transmitted and a signal having a wavelength for transmission is reflected. However, the reverse configuration is possible depending on which wavelength is used for transmission and reception.

[0036]

According to the present invention, in an optical integrated circuit in which the transmitting and receiving sections are mounted on the same substrate, the heat radiation of the transmitting section and the good receiving performance during simultaneous transmission and reception can be ensured. It can be applied to SDM and WDM transmission.

[Brief description of the drawings]

FIG. 1 is a diagram showing a mounting form of an optical integrated circuit for suppressing electric crosstalk between transmission and reception and a heat sink according to the present invention.

FIG. 2 is a diagram showing a mounting structure of the hybrid optical integrated circuit according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a mounting structure of a hybrid optical integrated circuit according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a mounting structure of a hybrid optical integrated circuit according to a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a mounting structure of a hybrid optical integrated circuit according to a fourth embodiment of the present invention.

FIG. 6 is a diagram illustrating a mounting structure of a hybrid optical integrated circuit according to a fifth embodiment of the present invention.

FIG. 7 is a diagram illustrating a mounting structure of a hybrid optical integrated circuit according to a sixth embodiment of the present invention.

FIG. 8 is a diagram showing a mounting structure of a conventional optical integrated circuit.

FIG. 9 is a diagram illustrating an electric crosstalk propagation path between transmission and reception in the integrated hybrid optical integrated circuit for transmission and reception.

[Explanation of symbols]

 1 Optical waveguide layer 2 Common substrate 3 Transmit electrode 4 Receive electrode 5 Light emitting element 6 Light receiving element 7 Bonding wire 8, 18, 22, 23 Heat sink

Continued on the front page F term (reference) 2H047 KA04 MA07 QA07 TA00 5F041 DA13 DA19 DA20 DA83 EE01 FF14 5F088 AA01 BA03 BA16 BB01 EA09 EA11 JA03 JA14 5F089 AA01 AC17 BC17 CA11

Claims (5)

[Claims] 1. An optical integrated circuit in which a light emitting element and a light receiving element are mounted on an insulating layer on the surface of a substrate, wherein the light emitting element and the light receiving element are formed so as to cover the rear surface of the substrate and expose the rear surface of the substrate under the light receiving element. An optical integrated circuit comprising a metal plate. 2. An optical integrated circuit in which a light-emitting element and a light-receiving element are mounted on an insulating layer on the surface of a substrate, wherein an optical integrated circuit is provided in which a plurality of metal plates are provided to cover the rear surface of the substrate. 3. The optical integrated circuit according to claim 1, wherein
An optical integrated circuit, wherein a conductive pattern is formed on the insulating layer and between the light emitting element and the light receiving element. 4. An optical integrated circuit, wherein said conductive pattern is connected to said metal plate by a wire. 5. An optical waveguide is formed in the insulating layer according to claim 1, and a mounting portion of a light emitting element and a light receiving element is recessed relative to an upper surface of the insulating layer so that the optical element optically couples with the optical waveguide. An optical integrated circuit having an irregular shape.