Optical Transmitter

Abstract

In regard to an optical transmitter in which an optical modulator and a driver IC therefor are mounted in a single package, the present invention discloses new configurations for improving the temperature dependence of the optical modulation output characteristics and a mounting form suitable for each configuration. An optical transmitter (13) comprises an optical modulator, a driver integrated circuit (driver IC) (12) that supplies a modulating electrical signal for the optical modulator, a first Peltier element (17) that controls the temperature of the optical modulator, and a second Peltier element (16) that controls the temperature of the driver IC, wherein the optical modulator and the driver IC are wire-connected and the temperature of the second Peltier element is set lower than the temperature of the first Peltier element.

Description

[Technical Field]

[0001] The present invention relates to an optical transmitter used in optical communications, and more particularly to an implementation form of an optical transmitter including a semiconductor optical modulator and its driver IC. [Background technology]

[0002] In order to cope with the rapid increase in traffic in communication networks, digital coherent optical transmission, which combines coherent communication methods and digital signal processing technology, has been introduced into optical fiber communication systems. Starting with the establishment of backbone network transmission technology of 100 Gbps per wavelength, currently even faster transmission speeds of 400 to 600 Gbps per wavelength are in practical use.

[0003] The digital coherent optical transmission described above uses an optical transmitter / receiver that integrates an optical receiver and an optical transmitter. Optical transmitter / receivers for systems with a transmission capacity of over 400 Gbps require broadband analog components such as radio frequency (RF) electrical circuits, and for example, optical modulators require a modulation bandwidth of 40 GHz or more. To reduce high frequency loss and downsize the device, which leads to broadband, for example, a configuration in which an RF driver IC and optical modulator are mounted in an integrated package on the transmitting side is attracting attention. This optical transmitter mounting configuration is called a High-Bandwidth Coherent Driver Modulator (HB-CDM: High-Speed ​​Driver Integrated Optical Modulator) It has also been standardized by the Optical Internetworking Forum (OIF) (Non-Patent Document 1). On the receiving side of the optical transceiver, a transimpedance amplifier (TIA) and an optical receiver are also mounted in an integrated package, which is also called an ICR (Integrated Coherent Receiver).

[0004] Turning our attention to materials for optical transmitting and receiving devices, semiconductor-based optical modulators are attracting attention as an alternative to conventional lithium niobate (LN) optical modulators due to their compact size and low cost. Compound semiconductors, such as InP, are mainly used for higher-speed modulation operations. Furthermore, for systems where compact size and low cost are important, research and development efforts are focused on Si-based optical devices.

[0005] Even the semiconductor optical modulators mentioned above have material-specific advantages and disadvantages. For example, in InP optical modulators, temperature control of the optical modulator chip is essential during operation to control the band-edge absorption effect. On the other hand, Si optical modulators have the advantage of not requiring temperature control, but their electro-optic effect is smaller than that of other material systems. This requires a longer electro-optic interaction length, which increases the device length and can result in increased high-frequency loss. There are many challenges to further increasing the speed and bandwidth of optical modulators, including packaging technologies for wider bandwidth and miniaturization.

[0006] The operating temperature (case temperature) of an HB-CDM optical transmitter is required to be in the range of at least -5° C. to 75° C. In order to ensure such an operating temperature, it has been common to mount only the optical modulator chip on a Peltier element, taking power consumption into consideration (Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2021 / 171599 [Non-patent literature]

[0008] [Non-Patent Document 1] OIF, Implementation Agreement for the High Bandwidth Coherent Driver Modulator (HB-CDM), [online], July 15, 2021, [Retrieved September 1, 2022], Internet<URL: https: / / www.oiforum.com / wp-content / uploads / OIF-HB-CDM-02.0.pdf> [Non-patent document 2] J. Ozaki et al., "500-Gb / s / λ Operation of Ultra-Low Power and Low-Temperature-Dependence InP-Based High-Bandwidth Coherent Driver Modulator," in Journal of Lightwave Technology, vol. 38, no. 18, pp. 5086-5091, 15 Sept.15, 2020, doi: 10.1109 / JLT.2020.2998466. Summary of the Invention [Problem to be solved by the invention]

[0009] However, conventional optical transmitters have had the problem of degradation of the high-frequency characteristics of the driver IC at high temperatures. Specifically, when the ambient temperature is high, the high-frequency bandwidth, peaking amount, and gain of the driver IC deteriorate. As optical transmitters become faster and wider in bandwidth, the impact of the degradation in signal quality due to the above-mentioned degradation can no longer be ignored. Therefore, there is a demand for optical transmitters that can maintain constant high-frequency characteristics regardless of changes in the ambient temperature.

[0010] In view of the above-mentioned problems, the present invention provides a novel configuration and implementation form of an optical transmitter that suppresses the temperature dependency of an optical transmitter including a driver IC, has excellent high-speed performance, and is capable of stable operation regardless of the ambient temperature. [Means for solving the problem]

[0011] One aspect of the present invention is an optical transmitter comprising an optical modulator, a driver integrated circuit (driver IC) that supplies a modulated electrical signal for the optical modulator, a first Peltier element that controls the temperature of the optical modulator, and a second Peltier element that controls the temperature of the driver IC, wherein the optical modulator and the driver IC are connected by wire, and the temperature of the second Peltier element is set lower than the temperature of the first Peltier element. [Effects of the Invention]

[0012] The present invention makes it possible to realize a novel configuration and implementation of an optical transmitter that suppresses the temperature dependency of an optical transmitter including a driver IC, has excellent high speed, and is capable of stable operation regardless of the ambient temperature. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional side view of a prior art HB-CDM optical transmitter implementation; [Figure 2] 1 is a side cross-sectional view of an implementation of an optical transmitter using HB-CDM according to the present invention. [Figure 3] 10A and 10B are diagrams illustrating height restrictions on wire connection points in an optical transmitter. [Figure 4] 10 is a cross-sectional side view of another implementation of an HB-CDM optical transmitter of the present invention. FIG. [Figure 5] FIG. 10 is a diagram for explaining restrictions on pad positions and the like on the circuit surface of the optical transmitter. [Figure 6] 10A and 10B are diagrams illustrating the density arrangement of Peltier elements in the optical transmitter of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] This invention proposes new configurations for improving the temperature dependency of the high frequency characteristics of an optical transmitter in which an optical modulator and its driver IC are packaged together, and mounting forms suitable for each configuration. The configurations for improving the temperature dependency include new forms of using a thermoelectric cooler (TEC) in the optical transmitter. Furthermore, new forms of using the TEC We also propose various implementations of driver ICs, optical modulator chips, and spatial optical components compatible with the above.

[0015] TECs, also known as thermoelectric coolers, are known as small cooling devices that use Peltier junctions. They are made up of n-type and p-type semiconductors and metals. When a direct current is passed through both sides of the plate-shaped element, heat is absorbed on one side and dissipated on the other. Reversing the direction of the current switches between heat absorption and heat dissipation, enabling precise, localized temperature control of ICs and electronic components. For simplicity's sake, the following explanation refers to the temperature regulator as a TEC and uses a Peltier element. Any device capable of controlling the temperature of a driver IC or optical modulator chip is not limited to Peltier elements.

[0016] In the following, we will first explain the problem of temperature dependency of high frequency characteristics in optical transmitters using an optical modulator in the form of HB-CDM of the prior art as an example, and then we will explain a novel configuration of the optical transmitter of the present invention that improves the temperature dependency of high frequency characteristics along with various implementation forms.

[0017] Fig. 1 is a side cross-sectional view showing the implementation of a conventional HB-CDM optical transmitter. Optical transmitter 100 conforms to HB-CDM specifications and houses a driver IC 102, an optical modulator chip 103, and lenses 112 and 113, which are spatial optical components, inside package housing 101 made of ceramic, metal, or a combination of these. More specifically, optical modulator chip 103 is mounted on the bottom inside housing 101 via subcarrier 104 on Peltier element 105. The optical modulator chip 103 has an output facet for modulated light at the right end of the drawing, and lenses 112 and 113 for optically coupling the modulated light with optical fiber 114 are also mounted on the subcarrier.

[0018] Adjacent to the optical modulator chip 103, a driver IC 102 is mounted on a metal block or ceramic material 106. Furthermore, the package housing 101 has a wiring board base 107 and a package wall 108 as the wall on the left side of the drawing, which, together with the package housing 101, separate the interior space of the optical transmitter from the outside. The optical transmitter 100 can also be configured so that the entire package is airtight.

[0019] A modulated electrical signal supplied from an external digital signal processor (DSP) is supplied to the optical modulator chip 103 via the wiring layer 109 and driver IC 102 of the wiring board base 107. The wiring layer 109 and the driver IC 102, and the driver IC 102 and the optical modulator chip 103, are connected by gold wires 110, 111, etc., respectively. In the case of a polarization-multiplexed IQ optical modulation system, the modulated electrical signal includes an I channel and a Q channel for each of the X and Y polarizations. When one channel is supplied as an electrical signal in a differential signal format, at least eight signal lines and a GND line are required for one optical modulator, but the modulation signal format is not limited to this. As described in Patent Document 1, the optical transmitter 100 shown in FIG. 1 can be mounted on a common device substrate together with an ICR package in which a receiving-side TIA and optical receiver are integrated, and a DSP, to form an optical transceiver.

[0020] Here, we again focus on the Peltier element 105 in the optical transmitter. Temperature control is essential for the optical modulator chip 103 fabricated on an InP substrate, and the Peltier element 105 controls the temperature to a predetermined operating temperature. As shown in Figure 1, the Peltier element 105 is sized to cover at least the entire area of ​​the optical modulator chip 103, and its position may overlap the area of ​​spatial optical components such as lenses. On the other hand, in the optical transmitter 100 of the prior art, it was considered unnecessary to control the temperature of the driver IC 102, and it was fixed inside the package by a member 106 such as a metal block or ceramic. When the external temperature (environmental temperature) of the optical transmitter 100 rises, that temperature rise becomes the operating temperature of the driver IC 102. Since the driver IC is also a heat source, taking into account the heat generated by the driver, the operating temperature of the driver IC is estimated to be about 5 to 10°C higher than the external temperature. When the maximum ambient temperature of an optical transceiver including the optical transmitter reaches 85°C, the temperature of the driver IC 102 itself also rises to at least 85°C. The driver IC also consumes a lot of power and generates heat, which means that the backside temperature of the driver IC exceeds the maximum ambient temperature of 85°C.

[0021] The driver IC's high-frequency electrical signal amplification characteristics (high-frequency characteristics) are temperature-dependent, and at high temperatures, the high-frequency bandwidth tends to decrease compared to room temperature. Conversely, at low temperatures, the high-frequency bandwidth tends to increase compared to room temperature. Thus, the high-frequency characteristics of the driver IC differ between low and high temperatures. The modulation signal supplied to the driver IC is optimized and compensated in various ways by a DSP at room temperature. However, dynamically updating this compensation in response to temperature fluctuations is a complex process and is not generally implemented. Because operation continues at a constant compensation state at room temperature, the compensation state of the modulation signal deviates from the optimal point when the temperature changes to a low or high temperature. This causes fluctuations and degradation in the optical transmission characteristics and waveform quality of the optical transmitter.

[0022] The IQ modulator of the optical modulator chip 103 is a linear modulator that preserves the amplitude and phase of the electrical signal, and fluctuations in the level and waveform quality of the modulated electrical signal directly affect the quality of the modulated output light. If the external temperature changes while the optical transmitter is operating, the optical modulator chip itself is maintained at a constant temperature because its temperature is controlled by a Peltier element, but the operating temperature of the driver IC changes. As a result, fluctuations in the level and quality of the HB-CDM modulated light occur, and temporal changes in the environmental temperature cause deterioration and instability in the transmission characteristics.

[0023] Degradation of characteristics due to environmental temperature on the high-frequency side of the electrical signal causes waveform distortion of the modulated signal, degrading the modulation accuracy of the modulated output light from the optical modulator. In an optical receiver receiving such degraded modulated light, a floor appears in the BER characteristics, leading to a degradation of the system's transmission characteristics.

[0024] With the increasing demand for wider bandwidth modulated electrical signals and the need for modulation bandwidths of 40 GHz or more, the impact of degradation of the high-frequency characteristics of driver ICs at high temperatures as described above cannot be ignored. This invention presents a new configuration and mounting form that improves the temperature dependency of high-frequency characteristics and optical transmission characteristics in an optical transmitter in which an optical modulator and its driver IC are integrally packaged.

[0025] FIG. 2 is a side cross-sectional view showing the implementation of an optical transmitter using HB-CDM according to the present invention. Similar to the conventional configuration shown in FIG. 1, the optical transmitter 10 of the present invention integrates an InP optical modulator chip 13, its driver IC 12, and other components inside a package housing 11 conforming to the HB-CDM. The left wall of the package housing 11 in the drawing includes a wiring board base 18 and a package wall 19, similarly defining the interior and exterior of the package. The difference from the conventional configuration shown in FIG. 1 is the use of a temperature-controlled electrochemical converter (TEC), i.e., a Peltier element. Unlike the Peltier element use in FIG. 1, the driver IC 12 is also mounted on a Peltier element 16. The Peltier element 16 of the driver IC 12 is separate and independent from the Peltier element 17 that controls the temperature of the optical modulator chip 13, and the optical transmitter 10 includes two Peltier elements.

[0026] The optical modulator chip 13 and lenses 23 and 24 are mounted on the Peltier element 17 via a subcarrier 14. The subcarrier 14 functions as a base for fixing and holding the optical modulator chip and spatial optical components. In addition, the subcarrier 14 has metal patterns formed thereon for wiring to connect with the DC wiring of the optical modulator chip, positioning markers for mounting the spatial optical components, and the like.

[0027] The material for the subcarrier 14, which will be mounted with the optical modulator chip 13, which is the target of temperature control, should have excellent thermal conductivity. Specifically, a ceramic substrate such as an AlN substrate is preferable. Because AlN substrates have similar material constants to InP, they are also compatible with InP-based optical modulators in terms of their behavior in response to temperature changes. For similar reasons and from the standpoint of material compatibility, it is desirable for the ceramic on top of the Peltier element 17 to be made of AlN. While Figure 2 depicts the subcarrier 14 as being made of a single-layer AlN structure, it can also be made of a multilayer AlN substrate. Using a multilayer substrate allows for flexible element and wiring layouts that make full use of multilayer wiring when there are many DC wirings to the optical modulator or when cross wiring is required to change the terminal order.

[0028] The driver IC 12, which is temperature-controlled independently of the optical modulator chip 13, is also preferably mounted on the Peltier element 16 via a holding member 15 so that its height is aligned with the optical modulator chip 13 and the RF terrace, which is the upper surface of the wiring board base 18. The holding member 15 can be a metal block or a ceramic substrate. Taking thermal conductivity into consideration, for example, if the driver IC 12 does not require DC wiring, a metal block such as a CuW block can be used, or if DC wiring for the driver is required, a ceramic such as an AlN substrate can be used. If an AlN substrate is used and the wiring to the driver IC is numerous and complex, a multilayer substrate can be used, similar to the subcarrier 14 for the optical modulator chip described above.

[0029] As mentioned above, the driver IC is a heat-generating element and was not considered to be a target for temperature control using a Peltier element. Driving power is required to operate the Peltier element, and there was no consideration given to using extra power for a heat-generating element. However, in order to realize a broadband optical transmitter, the inventors came up with the new idea of ​​adding temperature control to the heat-generating element.

[0030] As described above, the optical transmitter 10 of the present invention is equipped with two independently controlled Peltier elements 16 and 17, which enables independent temperature control of the optical modulator chip 13 and the driver IC 12. Although not shown in Figure 2, the two Peltier elements are connected to separate control current sources. Regarding the specific control temperatures of each component, since the modulation efficiency of InP optical modulators decreases if the temperature is too low, it is generally desirable to use them at around 45±10°C.

[0031] On the other hand, it is known that the high-frequency characteristics of the driver IC 12 are better at low temperatures than at high temperatures, so a lower temperature setting is desirable. However, setting the temperature too low increases the power consumption of the Peltier element, while limiting the improvement in the high-frequency characteristics of the driver IC. Therefore, operating the driver IC at, for example, 30±10°C, near room temperature, is the most appropriate from the perspective of balancing power consumption and high-frequency characteristics. By setting the optical modulator chip 13 and the driver IC 12 to different temperatures independently, an optical transmitter can be realized that can operate at the optimum conditions for each.

[0032] Therefore, the optical transmitter 10 of the present invention can be implemented as an optical transmitter comprising an optical modulator 13, a driver integrated circuit (driver IC) 12 that supplies a modulated electrical signal for the optical modulator, a first Peltier element 17 that controls the temperature of the optical modulator, and a second Peltier element 16 that controls the temperature of the driver IC, wherein the optical modulator and the driver IC are connected by wire, and the temperature of the second Peltier element is set lower than the temperature of the first Peltier element.

[0033] To improve heat dissipation by the Peltier element, the parts between which the temperature is controlled by the Peltier element must be mounted with conductive paste or solder with excellent thermal conductivity of 30 W / mK or more. For the purpose of managing the module manufacturing process temperature, the same conductive paste or solder may be used for all parts, or a combination of pastes or solders with different fixed temperatures may be used.

[0034] To suppress variations in adhesive thickness due to temperature changes, the spatial optical components such as lenses 23 and 24 are all mounted on the Peltier element 17. This minimizes variations in optical insertion loss due to deviations in the optical axis caused by temperature changes. The spatial optical components also include components for fixing the fiber and a PBC (Polarization Beam Combiner), etc.

[0035] While Fig. 2 shows an HB-CDM optical transmitter 10 as an example, similar effects can be achieved with other package configurations as long as the optical transmitter module has an integrated driver IC and optical modulator. Fig. 2 also shows an example in which wiring from a DSP that supplies a modulation signal to the driver IC 12 is connected by a flexible printed circuit board (FPC) on an RF terrace. That is, the wiring is connected to an FPC cable (not shown) at a metal pattern 20 on the top surface of the wiring board base 18 outside the optical transmitter. Compared to configurations using surface mount technology (SMT), the FPC interface has superior high-frequency characteristics because it does not require RF vias (VIAs).

[0036] Next, we will discuss the mounting structure for ensuring the high-frequency characteristics of the driver IC, optical modulator, etc. In the HB-CDM optical transmitter 10 shown in Figure 2, the electrode pads of the driver IC and the RF terrace are connected by wires 21 and 22, respectively, between the electrode pads of the driver IC and the electrode pads of the optical modulator. Longer wires increase the series inductance component, which causes LC resonance and shifts the roll-off frequency in the high-frequency characteristics to the lower side. Therefore, to suppress degradation of the high-frequency characteristics of the driver IC and achieve smooth connection, it is desirable for the wire inductance to be low. Therefore, in the optical transmitter 10, specifications are established for the height and planar directions of each part to be connected by wires.

[0037] Figure 3 is a diagram explaining the height restrictions on wire connection locations in an optical transmitter. Figure 2 shows an enlarged view of the RF terrace electrode 20, the driver IC 12, and the vicinity of the top surfaces of the optical modulator chip 13. The difference in height between wire-connected pads is 100 μm or less between the electrode pads of the driver IC and the electrode pads of the RF terrace, and between the electrode pads of the driver IC and the electrode pads of the optical modulator. This restriction is the minimum feasible range, taking into account variations in the thickness of each chip and variations in mounting components such as subcarriers.

[0038] The gap limit (≦50 μm) in the circuit plane direction of the driver IC 12 and optical modulator chip 13 shown in FIG. 3 will be described later. In FIG. 2, the driver IC 12 and optical modulator chip 13 are arranged so that one side of each is parallel to each other and are mounted so that they overhang the component directly below them. That is, one side of the driver IC 12 is mounted on the circuit plane so that it overhangs the optical modulator chip 13 from the support member 15, which is the component directly below the driver IC, and one side of the optical modulator chip is mounted on the circuit plane so that it overhangs the driver IC 12 from the subcarrier 14 directly below the chip. The overhanging mounting configuration of the ICs and chips described above is a device to prevent adhesives and other materials used to secure them from warping up onto the top surfaces of the ICs and chips. The temperature dependency of the high-frequency characteristics and optical transmission characteristics of the optical transmitter of the present invention is largely due to the temperature control of the driver IC by a Peltier element. Below we will explain a specific example of overhanging mounting, but if a technology emerges that allows parallel wire mounting without height differences between pads, there may be cases where the difference in height of the wire connection points shown in Figure 3 is not essential. Also, there may be cases where overhanging mounting is not essential if other structures or methods can be used that can effectively control warping of adhesives, etc.

[0039] For example, if the optical modulator chip and driver IC are designed to be 300 μm thick and the two Peltier elements 16 and 17 are the same height, then making the support member 15 and subcarrier 14 the same height will align the pad heights on the top surfaces of the driver IC and optical modulator chip. However, to minimize the wire length, it is best to reduce the thickness of the subcarrier on the optical modulator chip side by about 50 μm and mount the wire so that it extends from the optical modulator side to the driver IC side. Similarly, between the electrode pads of the driver IC and the electrode pads of the RF terrace, it is desirable to optimize the height of the support member 15 below the driver IC and the height of the Peltier element 16 so that the top surface of the driver IC is slightly lower than the RF terrace.

[0040] Furthermore, if the driver IC 12 is very thin, e.g., 100 μm thick, and the optical modulator chip is designed to be 300 μm thick, and the two Peltier elements 16 and 17 are the same height, then even if the support member 15 and subcarrier 14 are set to the same height, a height difference of 200 μm will result between the top surfaces of the two chips. In such a case, the heights of the support member 15 and subcarrier 14 must be adjusted. For example, if a 250 μm metal block is added below the driver IC, the height of the driver IC 12's top surface from the common top surface of the Peltier elements will be 350 μm, and the height of the optical modulator chip will be 300 μm. As a result, the height difference between the driver IC 12 and the optical modulator chip will be 50 μm, creating an ideal situation in which the top surface of the driver IC is higher. Naturally, the height of the RF terrace must be adjusted to match the height of the driver IC 12's top surface.

[0041] As mentioned above, it should be noted that if technology becomes available that allows wire mounting between pads of the same height, the height difference between the top surfaces of the RF terrace, driver IC, and optical modulator chip described above may not be necessary.

[0042] Figure 4 is a side cross-sectional view showing another implementation of an HB-CDM optical transmitter according to the present invention. Compared to the optical transmitter 10 shown in Figure 2, the optical transmitter 30 has a reduced number of components for cost reduction. The driver IC 12 and optical modulator chip 13 are directly mounted on the Peltier elements 16 and 17, respectively. The height-adjustable support member 15 and subcarrier 14 described in conjunction with Figure 3 are omitted. The simplified configuration shown in Figure 4 also allows for the height difference between the top surfaces of the chips to be adjusted by changing the heights of the two Peltier elements 16 and 17. The optical transmitter 30 configuration shown in Figure 4 requires fewer components and fewer parts requiring adhesive, which can be expected to improve thermal resistance and reduce power consumption due to the reduced adhesive area.

[0043] In Figure 4, the driver IC 12 and optical modulator chip 13 are also mounted with their respective sides parallel to one another and overhanging from the component directly below. That is, one side of the driver IC 12 is mounted on the circuit surface so that it overhangs the optical modulator chip 13 from the Peltier element 16, which is the component directly below the driver IC, and one side of the optical modulator chip is mounted on the circuit surface so that it overhangs the driver IC from the Peltier element 17, which is the component directly below the chip. In the case of Figure 4, too, the temperature control of the driver IC by the Peltier element contributes significantly to the improvement of the temperature dependency of the high-frequency characteristics and optical transmission characteristics. Therefore, even without the difference in the height direction of the wire connection points in Figure 3 or the overhanging mounting in Figure 4, it is still possible to realize an optical transmitter that can operate stably regardless of the ambient temperature.

[0044] Figure 5 illustrates limitations on pads and other components on the circuit surface of an optical transmitter. The gap between the optical modulator chip 13 and the driver IC 12 on the circuit surface directly affects the wire length, so it is desirable to minimize the gap between the two chips. Considering the ease of assembly and the risk of short circuits, it is desirable to control the gap to 50 μm or less. Furthermore, controlling the gap between the two chips alone would not be effective in shortening the wire length if the electrode pads were located far from the chip edges. Therefore, the electrode pads were located no more than 50 μm from each chip edge. A distance of 50 μm or less from the chip edge to the electrode pad is easily achievable through standard dicing and cleaving processes. As described in Figures 2 and 4, one side of the driver IC is mounted on the circuit surface so that it protrudes toward the optical modulator chip relative to the component directly below the driver IC, and one side of the optical modulator chip can also be mounted on the circuit surface so that it protrudes toward the driver IC relative to the component directly below the chip.

[0045] As an example, Figure 5 shows the output electrode pads on the driver IC side and the input electrode pads on the optical modulator chip side. The output electrode pads on the driver IC side are GSGSG and those on the optical modulator chip are GSSG, but the shapes of the respective electrode pads are the same in layouts other than those shown in Figure 5. In Figure 5, in order to reduce the wire inductance, only the connection wires between the signal electrode pads are connected with two wires. From the perspective of reducing inductance, it is effective to use not only ball wires as in this figure, but also wide ribbon wires or other configurations that further reduce inductance.

[0046] Regarding the gap in the circuit plane between the driver IC and the RF terrace, the influence of the inductance at these connections is smaller than the inductance between the driver IC and the optical modulator chip, so it is desirable to keep this gap, for example, to 100 μm or less.

[0047] In the above description, the lenses 23 and 24 are mounted as spatial optical components, but the present invention also includes fiber fixing members, PBCs, and the like.

[0048] FIG. 6 is a diagram illustrating the density arrangement of Peltier elements in the optical transmitter of the present invention. A Peltier element has many n-type and p-type semiconductor elements arranged between upper and lower metal surfaces, allowing heat to be transferred between the two surfaces as a whole. Therefore, the arrangement density of the semiconductor elements within the Peltier element can be set according to the heat generation amount of the object to be temperature controlled. Considering the heat generation amount of each part within the optical transmitter, the driver IC generates the most heat, followed by the optical modulator chip and the spatial optical components. Specifically, the element density of the Peltier elements should be set so that the mounting area of ​​the driver IC > the mounting area of ​​the optical modulator chip > the mounting area of ​​the spatial optical components.

[0049] 6, the Peltier element 16 that controls the driver IC should have the highest element density. Furthermore, within the Peltier element 17 that controls the optical modulator chip, the region directly below the optical modulator may have a medium density, while the region 17-2 for spatial optical components, etc. may have a low density.

[0050] As explained above in detail, the optical transmitter of the present invention can suppress the temperature dependency of the optical modulation output characteristics and realize a novel configuration and implementation of an optical transmitter with excellent high speed. [Industrial Applicability]

[0051] The present invention can be used in optical communication networks.

Claims

1. 1. An optical transmitter, comprising: an optical modulator; a driver integrated circuit (driver IC) that provides a modulated electrical signal for the optical modulator; a first Peltier element for controlling the temperature of the optical modulator; a second Peltier element for controlling the temperature of the driver IC; Equipped with The optical modulator and the driver IC are connected by wires; the temperature of the second Peltier element is set lower than the temperature of the first Peltier element; a spatial optical component is mounted on the first Peltier element on the opposite side of the optical modulator chip from the driver IC; The optical transmitter is characterized in that the first Peltier element and the second Peltier element are configured such that the in-plane density of n-type semiconductor elements and p-type semiconductor elements is such that: the second Peltier element > the mounting area of ​​the optical modulator chip of the first Peltier element > the mounting area of ​​the spatial optical component of the first Peltier element.

2. An optical transmitter, an optical modulator; a driver integrated circuit (driver IC) that provides a modulated electrical signal for the optical modulator; a first Peltier element for controlling the temperature of the optical modulator; a second Peltier element for controlling the temperature of the driver IC; Equipped with The optical modulator and the driver IC are connected by wires; the temperature of the second Peltier element is set lower than the temperature of the first Peltier element; The optical modulator chip and the driver IC are packaged in a high-speed driver integrated optical modulator (HB-CDM) type package; an electrode pad based on a differential signal interface is formed in an electrical signal path of an input section of the package, the driver IC, and the optical modulator chip; The difference in height between the top surface of the RF terrace on which the radio frequency (RF) electrode pads of the input section are formed and the top surface of the driver IC is 100 μm or less, the gap in the circuit surface between the RF terrace and the driver IC is 100 μm or less, and the RF electrode pads of the RF terrace and the electrode pads of the driver IC are wire-connected. An optical transmitter comprising:

3. 3. The optical transmitter according to claim 1, wherein the difference in height between the top surface of the optical modulator mounted on the first Peltier element and the top surface of the driver IC mounted on the second Peltier element is 100 μm or less.

4. one side of the driver IC is mounted on a member directly below the driver IC within a circuit plane, protruding toward the chip side of the optical modulator; One side of the optical modulator chip is mounted on a circuit surface so as to protrude toward the driver IC from a member directly below the chip, a gap between the one side of the driver IC and the one side of the optical modulator chip is 50 μm or less; 3. The optical transmitter according to claim 1, wherein the distance from the one side of the driver IC to the electrode pad is 50 μm or less, and the distance from the one side of the optical modulator chip to the electrode pad is 50 μm or less.

5. The member directly below the driver IC is a metal block or ceramic, 5. The optical transmitter according to claim 4, wherein the member directly below the chip is a subcarrier made of aluminum nitride (AlN).

6. the temperature of the first Peltier element is set to 45±10°C; 3. The optical transmitter according to claim 1, wherein the temperature of the second Peltier element is set to 30.+-.10.degree.

7. The optical modulator is configured by an Inp, At least one of the first Peltier element and the second Peltier element has an upper surface made of aluminum nitride (AlN), 3. The optical transmitter according to claim 1, wherein a paste or solder layer having a thermal conductivity of 30 W / mK or more is provided between the first Peltier element and the optical modulator chip, and between the second Peltier element and the driver IC.

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