WO2024075168A1 - 光送信器 - Google Patents

光送信器 Download PDF

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Publication number
WO2024075168A1
WO2024075168A1 PCT/JP2022/037031 JP2022037031W WO2024075168A1 WO 2024075168 A1 WO2024075168 A1 WO 2024075168A1 JP 2022037031 W JP2022037031 W JP 2022037031W WO 2024075168 A1 WO2024075168 A1 WO 2024075168A1
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WO
WIPO (PCT)
Prior art keywords
driver
optical
peltier element
optical modulator
subcarrier
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/JP2022/037031
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English (en)
French (fr)
Japanese (ja)
Inventor
常祐 尾崎
義弘 小木曽
光映 石川
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NTT Inc
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Nippon Telegraph and Telephone Corp
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Application filed by Nippon Telegraph and Telephone Corp filed Critical Nippon Telegraph and Telephone Corp
Priority to JP2024555490A priority Critical patent/JPWO2024075168A1/ja
Priority to PCT/JP2022/037031 priority patent/WO2024075168A1/ja
Priority to US19/115,384 priority patent/US20260104602A1/en
Publication of WO2024075168A1 publication Critical patent/WO2024075168A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0102—Constructional details, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
    • G02F1/017—Structures with periodic or quasi periodic potential variation, e.g. superlattices, quantum wells
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K7/00—Constructional details common to different types of electric apparatus
    • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
    • H05K7/2039—Modifications to facilitate cooling, ventilating, or heating characterised by the heat transfer by conduction from the heat generating element to a dissipating body

Definitions

  • the present invention relates to an optical transmitter used in optical communications. More specifically, the present invention relates to an implementation form of an optical transmitter that includes a semiconductor optical modulator and its driver IC.
  • an optical transceiver in which an optical receiver and an optical transmitter are integrated is used.
  • broadband analog components such as radio frequency (RF) electrical circuits are required.
  • RF radio frequency
  • an optical modulator requires a modulation bandwidth of 40 GHz or more.
  • HB-CDM High-Bandwidth Coherent Driver Modulator
  • ICR Integrated Coherent Receiver
  • 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 faster modulation operations.
  • Si-based optical devices Furthermore, in systems where compact size and low cost are important, research and development is focused on Si-based optical devices.
  • the semiconductor optical modulators mentioned above have their own advantages and disadvantages specific to each material.
  • temperature control of the optical modulator chip is essential during operation in order to control the band-edge absorption effect.
  • a Si optical modulator has the advantage of not needing temperature control, but has a smaller electro-optic effect than other material systems. This makes it necessary to lengthen the electro-optic interaction length, which can result in increased high-frequency loss as a result of the device length increasing.
  • the operating temperature (case temperature) of an optical transmitter using HB-CDM must be in the range of at least -5°C to 75°C. In order to ensure this operating temperature, it has been common to only mount the optical modulator chip on a Peltier element, taking into account power consumption (Patent Document 1).
  • the present invention provides a new 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 environmental temperature.
  • 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, a second Peltier element that controls the temperature of the driver IC, and a subcarrier that includes electrical wiring between the optical modulator and the driver IC and is mounted on the first Peltier element and the second Peltier element, the optical modulator chip and the driver IC being flip-chip mounted in a face-down configuration, and the temperature of the second Peltier element being set lower than the temperature of the first Peltier element.
  • driver IC driver integrated circuit
  • the present invention makes it possible to realize a new configuration and implementation form of an optical transmitter that suppresses the temperature dependency of the optical transmitter including the driver IC, has excellent speed, and is capable of stable operation regardless of the environmental temperature.
  • FIG. 1 is a cross-sectional side view of a prior art HB-CDM optical transmitter implementation.
  • 1 is a side cross-sectional view of an implementation of an optical transmitter using HB-CDM of the present invention.
  • 10A and 10B are diagrams for explaining limitations in the height direction of wire connection points in an optical transmitter;
  • FIG. 13 is a top view of a modified implementation of the optical transmitter of the present invention.
  • 11 is a side cross-sectional view of another implementation of the optical transmitter of the present invention.
  • FIG. 11 is a side cross-sectional view of yet another implementation of the optical transmitter of the present invention.
  • FIG. 4A and 4B are diagrams for explaining the density arrangement of Peltier elements in the optical transmitter of the present invention.
  • the present invention presents new configurations for improving the temperature dependency of the high-frequency characteristics of an optical transmitter in an optical transmitter in which an optical modulator and its driver IC are integrated into a package, and mounting forms compatible with each configuration.
  • the configuration for improving the temperature dependency includes a new usage form of a temperature regulator (TEC: ThermoElectric Cooler) in the optical transmitter.
  • TEC ThermoElectric Cooler
  • various mounting forms of the driver IC, optical modulator chip, and spatial optical components compatible with the new usage form of the TEC are also proposed.
  • TECs are also known as thermoelectric coolers, and are known as small cooling devices that use Peltier junctions. TECs are made up of n-type semiconductors, p-type semiconductors, and metals, and 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 dissipation, allowing for localized and precise temperature control of ICs and electronic components. For simplicity's sake, in the following explanation, the temperature regulator will be referred to as a TEC and described as a Peltier element. Any device that can control the temperature of a driver IC or optical modulator chip is not limited to one that uses a Peltier element.
  • FIG. 1 is a side cross-sectional view showing the implementation of an optical transmitter using HB-CDM, a conventional technology.
  • the optical transmitter 100 contains a driver IC 102, an optical modulator chip 103, and lenses 112 and 113, which are spatial optical components, inside a package housing 101 made of ceramic, metal, or a combination of these. More specifically, the optical modulator chip 103 is mounted on the inside bottom surface of the housing 101 via a subcarrier 104 on a Peltier element 105. The right end of the optical modulator chip 103 in the drawing has an output facet for modulated light, and lenses 112 and 113 for optically coupling the modulated light to an optical fiber 114 are also mounted on the subcarrier.
  • a driver IC 102 is mounted on a metal block or ceramic material 106 adjacent to the optical modulator chip 103.
  • the package housing 101 has a wiring board base 107 and a package wall 108 as the left wall in the drawing, which, together with the package housing 101, separate the outside from the internal space of the optical transmitter.
  • the optical transmitter 100 can also be constructed so that the entire package is airtight.
  • the 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.
  • the modulated electrical signal includes an I channel and a Q channel for each of the X polarization and the Y polarization.
  • one channel is supplied as an electrical signal in a differential signal format, at least eight signal wirings and a GND wiring are required for one optical modulator, but the modulated signal format is not limited to this.
  • the optical transmitter 100 shown in FIG. 1 can be mounted on a common device substrate together with an ICR package in which the receiving side TIA and optical receiver are integrated, and a DSP, to form an optical transmitting and receiving device.
  • 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 FIG. 1, the Peltier element 105 has a size that covers 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.
  • the optical transmitter 100 of the conventional technology it was considered that temperature control of the driver IC 102 was not necessary, and it was fixed in the package by a member 106 such as a metal block or ceramic. If the external temperature (ambient temperature) of the optical transmitter 100 rises, the increased temperature becomes the operating temperature of the driver IC 102.
  • the driver IC is also a heat source, so considering the heat generated by the driver, it is estimated that the operating temperature of the driver IC is about +5 to +10°C higher than the external temperature. If the maximum ambient temperature at which an optical transmission/reception device including an optical transmitter is used is 85°C, the temperature of the driver IC 102 itself is at least 85°C or higher. The driver IC also consumes a large amount of power, and the driver IC itself generates heat. This means that the backside temperature of the driver IC will exceed the maximum environmental temperature of 85°C due to the heat generated by the driver IC.
  • the driver IC has temperature-dependent amplification characteristics (high frequency characteristics) of high frequency electrical signals, and at high temperatures the high frequency band tends to decrease compared to room temperature. Conversely, at low temperatures the high frequency band 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 the DSP at room temperature. However, dynamically updating such compensation in line with 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 state changes to a low or high temperature. This causes fluctuations and deterioration in the optical transmission characteristics and waveform quality of the optical transmitter.
  • 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 in operation, the optical modulator chip itself is maintained at a constant temperature because the 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 the transmission characteristics deteriorate and become unstable due to changes in the environmental temperature over time.
  • the deterioration of characteristics due to the 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.
  • a floor appears in the BER characteristics, leading to a deterioration in the transmission characteristics of the system.
  • the present invention presents a new configuration and implementation 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 packaged together.
  • FIG. 2 is a side cross-sectional view showing the mounting form of an optical transmitter using the HB-CDM of the present invention.
  • an InP optical modulator chip 13 its driver IC 12, and other components are integrally configured inside a package housing 11 along the HB-CDM, as in the conventional technology configuration shown in FIG. 1.
  • the package housing 11 has a wiring board base 19 and a package wall 20 as the wall on the left side of the drawing, and the configuration that divides the inside and outside of the package is also similar.
  • the difference from the conventional technology configuration of FIG. 1 is the use of the TEC, i.e., the Peltier element, which controls the temperature.
  • the driver IC 12 is also mounted on the Peltier element 17.
  • the Peltier element 17 of the driver IC 12 is separate and independent from the Peltier element 18 that controls the temperature of the optical modulator chip 13, and the optical transmitter 10 has two Peltier elements.
  • a driver IC 12 is mounted on the two Peltier elements 17 at a position corresponding to the Peltier element 17, and an optical modulator chip 13 and lenses 23, 24 are mounted on the two Peltier elements 17, 18 at a position corresponding to the Peltier element 18, via a single subcarrier 14.
  • the subcarrier 14 functions as a base for flip-chip mounting the optical modulator chip 13 and the driver IC 12 across the two Peltier elements 17, 18. Therefore, the heights of the two Peltier elements 17, 18 must be the same so that the subcarrier is not mounted at an angle.
  • a face-down mounting of the optical modulator chip 13 and the driver IC 12 is performed on the subcarrier 14 using Au pillars/bumps or Cu pillars/bumps.
  • the driver IC 12 and the optical modulator chip 13 are mounted so that their respective electrode pad surfaces face downwards in the drawing, i.e., toward the top surface of the subcarrier 14.
  • all spatial optical components such as lenses 23 and 24 are mounted on the subcarrier 14 and positioned within the area of the Peltier element 18.
  • underfill materials 16-1 and 16-2 with excellent thermal conductivity can be embedded between the flip-chip mounted driver IC 12 and optical modulator chip 13 and the subcarrier 14 for temperature control using Peltier elements.
  • an underfill material with a thermal conductivity of 3 W/mK or more is desirable.
  • the introduction of underfill materials 16-1 and 16-2 is also very effective in terms of increasing the bonding strength with the subcarrier 14.
  • Underfill material can also be omitted.
  • Underfill material is a dielectric and has a certain dielectric constant and dielectric dissipation factor, which may lead to loss in high-frequency wiring such as in optical modulators. Please note that depending on the high-frequency band and baud rate required for the optical modulator, it is possible to prioritize high-frequency characteristics over temperature stability and bonding strength and not use underfill material.
  • wiring for connecting to the DC wiring of the driver IC 12 and the optical modulator chip 13, RF lines for high-frequency connection between the driver IC 12 and the optical modulator chip 13, and positioning markers for mounting spatial optical components are formed by metal patterns.
  • thermocontrol by the two Peltier elements 17, 18 is performed across the subcarrier 14, and from the perspective of mounting the driver IC 12 which generates a large amount of heat, it is desirable to use a material with as good thermal conductivity as possible for the subcarrier 14.
  • a ceramic substrate such as an AlN substrate is preferable. Since the material constant of an AlN substrate is close to that of InP, it also works well with InP-based optical modulators in terms of behavior in response to temperature changes. For the same reason, and from the perspective of material compatibility, it is desirable for the ceramic on the top surface of the Peltier element 17 to be made of AlN.
  • the subcarrier 14 is depicted as being made of a single layer of AlN, but it can also be a multi-layer AlN substrate.
  • a multi-layer substrate By using a multi-layer substrate, it is possible to implement a flexible element and wiring layout that makes full use of multi-layer wiring when there are a large number of DC wirings to the optical modulator or when cross wiring is required to change the order of the terminals.
  • RF design by making the subcarrier 14 into a multi-layer wiring, a GND layer can be provided adjacent to the wiring layer, and the line width can be made narrower, allowing for high-density wiring, and increasing the freedom of layout.
  • All spatial optical components such as lenses 23 and 24 are mounted on the Peltier element 17 to prevent thickness variations caused by temperature changes in the adhesive. This makes it possible to minimize variations in optical insertion loss caused by shifts in the optical axis due to temperature changes.
  • Spatial optical components also include components for fixing the fiber and a PBC (Polarization Beam Combiner), etc.
  • the waveguide that emits the modulated output light of the optical modulator chip 13 is located close to the subcarrier 14 in the height direction.
  • the height of the Au/Cu pillar, and the size of the lens it may be difficult to mount the lens. Such cases will be described later as another embodiment.
  • the driver IC is a heating element and was not considered to be a target for temperature control by a Peltier element. Driving power is required to operate the Peltier element, and no consideration was given to using extra power for a heating element.
  • the inventors came up with the new idea of adding temperature control to the heating element.
  • the optical transmitter 10 of the present invention is equipped with two independently controllable Peltier elements 17, 18 as described above, which allows independent temperature control of the optical modulator chip 13 and the driver IC 12. Although not shown in FIG. 2, the two Peltier elements are connected to separate control current sources. As for the specific control temperatures of each part, it is generally desirable to use an InP optical modulator at around 45 ⁇ 10°C, since the modulation efficiency decreases if the temperature is too low.
  • the high frequency characteristics of the driver IC 12 are better at low temperatures than at high temperatures, so the lower the set temperature, the more desirable it is.
  • setting the temperature too low increases the power consumption of the Peltier element, but there is only a limited improvement in the high frequency characteristics of the driver IC. Therefore, from the perspective of balancing power consumption and high frequency characteristics, it is most appropriate to operate the driver IC at, for example, 30 ⁇ 10°C, which is close to room temperature.
  • the optical transmitter 10 of the present invention therefore comprises 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 18 that controls the temperature of the optical modulator, a second Peltier element 17 that controls the temperature of the driver IC, and a subcarrier 14 that includes electrical wiring between the optical modulator and the driver IC and is mounted on the first Peltier element and the second Peltier element, the optical modulator chip and the driver IC being flip-chip mounted in a face-down configuration, and the temperature of the second Peltier element being set lower than the temperature of the first Peltier element.
  • driver IC driver integrated circuit
  • the space between the two Peltier elements 17, 18 and the subcarrier 14 must be implemented with conductive paste or solder with excellent thermal conductivity of 30 W/mK or more.
  • conductive paste or solder with excellent thermal conductivity of 30 W/mK or more.
  • the same conductive paste or solder may be used for all of them, or a combination of pastes or solders with different fixed temperatures may be used.
  • two Peltier elements 17, 18 control the temperature of the driver IC and the optical modulator chip via a common subcarrier 14. Because the driver IC and the optical modulator chip are connected via the subcarrier 14, the two temperature controls cannot be performed completely independently. However, the Peltier element 17 significantly reduces the risk of the driver IC 12 becoming overheated, improving the high frequency characteristics. In addition, by using a single subcarrier 14, material costs can be reduced and the mounting process can be simplified. For example, in order to achieve independent control, it is also effective to provide a thermal isolation groove on either the top or bottom surface of the subcarrier 14, or on both the top and bottom surfaces, as described below, to achieve thermal isolation between the optical modulator and the driver IC.
  • an optical transmitter 10 in HB-CDM form is shown as an example, but similar effects can be obtained with other package forms as long as the optical transmission module has an integrated driver IC and optical modulator.
  • an example is shown 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 metal pattern 21 on the top surface of the wiring board base 19 on the outside of the optical transmitter is connected to an FPC cable (not shown).
  • FPC flexible printed circuit board
  • the FPC interface has superior high-frequency characteristics because it does not require RF vias (VIAs), etc.
  • the high-frequency mounting structure for ensuring the high-frequency characteristics of the optical transmitter including the driver IC and optical modulator.
  • the electrode pads of the driver IC and the electrode pads of the optical modulator are connected by high-frequency wiring of the subcarrier 14, and the driver IC 12 and the optical modulator chip 13 are flip-chip mounted using AU pillars and Cu pillars.
  • the electrode pads of the driver IC and the electrode pads of the RF terrace are connected by wires 22.
  • the inductance of the electrical signal path is what contributes most to the high-frequency characteristics of an optical modulator. For example, if the wire is long, the series inductance component increases, causing the roll-off frequency in the high-frequency characteristics to shift to the lower side due to LC resonance. Therefore, to improve high-frequency characteristics, it is desirable to have a low series inductance.
  • the driver IC and optical modulator chip are flip-chip mounted, which reduces the inductance of the electrical signal path to about 1/5 to 1/10 compared to normal wire connections, making it possible to achieve a broadband.
  • further regulations are set for the height position of the wire connection part and the distance between the chips.
  • Figure 3 is a diagram explaining the height restriction of the wire connection point in the optical transmitter. It shows an enlarged view of the electrode 21 of the RF terrace, the driver IC 12, and the vicinity of the top surface of the optical modulator chip 13 in Figure 2.
  • the inductance between the electrode of the RF terrace and the electrode of the driver IC has a smaller effect on the characteristics than the inductance between the electrode of the driver IC and the electrode of the optical modulator, but it is desirable to make it as small as possible.
  • the height of the Peltier elements 17 and 18 may be changed, the thickness of the subcarrier 14 may be changed, or the height of the wiring board base 19 of the RF terrace may be changed.
  • the distance between the driver IC 12 and the optical modulator chip 13 must be at least 500 ⁇ m. By ensuring a gap of 500 ⁇ m or more between the IC and the chip, it becomes easier for jigs and the like to access the optical transmitter during the mounting process. Taking into account the deterioration of the high frequency characteristics mentioned above, the distance between the driver IC 12 and the optical modulator chip 13 must be kept to a maximum of 5 mm or less.
  • differential drive which can suppress amplitude more than single-ended drive
  • the modulated electrical signal is a differential signal interface from the driver to the optical modulator.
  • the RF wiring between the driver IC 12 and the optical modulator chip 13 in the subcarrier 14 is also laid out using differential lines such as GSGSG or GSSG (S: signal, G: GND). Since high-frequency characteristics may deteriorate if there is a bend in the RF differential line, it is desirable to align the positions of the electrode pads of the driver and modulator as much as possible when laying out the line, and further to form the RF differential line in a straight line.
  • the high frequency wiring for connecting the driver IC 12 and the optical modulator chip 13 in the subcarrier 14 is best to form the high frequency wiring for connecting the driver IC 12 and the optical modulator chip 13 in the subcarrier 14 on the top surface of the subcarrier 14.
  • the underfill material will end up on the high frequency signal line. It is difficult to control with high precision how much the underfill material protrudes around the chip. This can lead to asymmetry in the pair of high frequency signal lines (e.g. I+ and I-) formed by the differential line, and variation between channels, which can adversely affect the high frequency characteristics and transmission characteristics.
  • FIG. 4 is a top view showing a modified embodiment of the mounting form of the optical transmitter of the present invention. It corresponds to a top view of the circuit surface inside the module, with the housing 11 of the optical transmitter 10 shown in FIG. 2 cut away.
  • grooves 26-1 and 26-2 are formed on the top surface of the subcarrier 14, as shown by the dotted lines.
  • the high-frequency wiring of the subcarrier 14 is configured in the dotted line area 27 between the driver IC 12 and the optical modulator chip 13.
  • the driver IC 12 and the optical modulator chip 13 have electrode pads for RF connection formed around their respective peripheries.
  • a linear groove 26-2 is formed only on one side of the high-frequency wiring area 27 for the driver IC 12, and a rectangular groove 26-1 is formed near the periphery 4 of the optical modulator chip 13.
  • the shape of the groove is not limited to the configuration shown in FIG. 4, and can be changed according to the properties of the underfill material and the shape of the wiring on the subcarrier that should be avoided.
  • the groove 26-2 of the driver IC 12 is only on one side on the optical modulator chip side, but it may be formed in a rectangular shape around the periphery 4 of the driver IC.
  • FIG. 4 In addition to the configuration of FIG.
  • a linear groove may be added to one side of the RF terrace side of the driver IC 12, that is, the side of the wiring board base 19. Furthermore, in FIG. 4, a rectangular groove 26-1 is formed near the periphery 4 of the optical modulator chip 13, but the groove may be formed only on two sides, the driver IC side and the lens side described below.
  • the linear groove 26-2 of the driver IC 12 and the rectangular groove 26-1 of the optical modulator chip 13 on the driver IC side also serve as a thermal isolation groove between the optical modulator chip and the driver IC. That is, a groove can be provided on the surface of the subcarrier 14 near at least one of the opposing sides of the driver IC 12 and the optical modulator chip 13.
  • the above-mentioned groove improves the independence of temperature control, significantly mitigates the high temperature state of the driver IC 12, and improves the high frequency characteristics.
  • a groove can also be formed in the region 27 because the high frequency wiring can be formed in the inner layer.
  • this groove can also serve as a thermal isolation groove.
  • the underfill material rises up near the chip end face on the lens side of the optical modulator chip 13, the underfill material may adhere to the emission end face, deteriorating the optical coupling with the lenses 23 and 24.
  • the groove on one side of the rectangular groove 26-1 on the lens 23 side of the optical modulator chip 13 shown in FIG. 4 is also effective in avoiding such optical coupling problems.
  • the subcarrier 14 is formed in a multi-layer structure, it is possible to avoid the effects of the above-mentioned underfill material by configuring the high-frequency line as an inner layer of the subcarrier. Also, if the high-frequency wiring is configured as an inner layer, a groove can be formed at any location on the top surface of the subcarrier between the optical modulator chip and the driver IC. Needless to say, sufficient consideration must be given to the effects on disconnection of the inner layer wiring and characteristic impedance. On the other hand, when designing high-frequency wiring with the same line impedance, the signal line width becomes narrower in the inner layer wiring due to the influence of the effective dielectric constant of the subcarrier. Furthermore, since it is also affected by the dielectric loss tangent of the subcarrier, it is desirable to have the wiring pattern on the outermost surface of the subcarrier 14 when only considering the loss of the high-frequency line.
  • the lenses 23 and 24 are arranged on the opposite side of the optical modulator chip 13 to the driver IC 12.
  • at least one lens may be arranged on the upper or lower side of the optical modulator chip 13 when viewed from the top view of FIG. 4.
  • the PBC may be arranged on a different side from the driver IC. That is, the spatial optics is mounted above the Peltier element 18 on a side of the optical modulator chip other than the side facing the driver IC 12. A groove for allowing excess underfill material to escape may be formed near the side of the optical modulator chip that corresponds to the spatial optics.
  • FIG. 5 is a side cross-sectional view showing another implementation of an optical transmitter using HB-CDM of the present invention.
  • the optical transmitter 30 in Fig. 5 differs from the configuration of the optical transmitter 10 in Fig. 2 in terms of the mounting form of the lenses 23, 24.
  • the waveguide that emits the modulated output light of the optical modulator chip 13 is usually located near the bottom surface of the chip, which is close to the subcarrier 14 in the height direction.
  • the optical axis may be misaligned and the lens may not be mounted with sufficient optical coupling.
  • the optical transmitter 30 in FIG. 5 can facilitate optical coupling of the lens by changing the thickness of the subcarrier between the mounting area of the driver IC and the optical modulator chip and the mounting area of the spatial optical components such as lenses.
  • the subcarrier part 14-2 in the mounting area of the lenses 23 and 24 is thinner than the subcarrier part 14-1 in the area of the driver IC 12 and the optical modulator chip 13. It is desirable to make the thickness of the subcarrier for the part 14-2 where the spatial optical components are mounted equal to or greater than the radius of the lens. For example, assuming that the diameter of the lens is 500 ⁇ m, the subcarrier part 14-2 needs to be lowered from the top surface by at least 250 ⁇ m or more to make it thinner.
  • the thickness of the underfill materials 16-1 and 16-2 By controlling the thickness of the underfill materials 16-1 and 16-2 to be the same height as the Au pillar or Cu pillar, it is possible to align the optical axis from the emission point of the optically modulated output light to the optical fiber 25.
  • the height of the subcarrier can also be changed by using the subcarrier as a multilayer board and reducing the number of layers of the subcarrier part 14-2 in the mounting area of the lenses 23 and 24.
  • FIG. 6 is a side cross-sectional view showing yet another implementation of an optical transmitter using the HB-CDM of the present invention.
  • the subcarrier is divided into two, with the subcarrier 14 being the mounting area for the driver IC and optical modulator chip, and the subcarrier 15 being the mounting area for spatial optical components such as lenses.
  • This configuration in which the subcarrier is divided into two makes it easier to adjust the height of the lenses 23 and 24, and allows the optical axis to be aligned from the emission point of the optically modulated output light to the optical fiber 25.
  • the driver IC 12 and the optical modulator chip 13 are temperature-controlled by corresponding separate Peltier elements 17 and 18, respectively, via a single subcarrier 14, just like the configurations of the optical transmitters 10 and 30 of FIG. 2 and FIG. 5.
  • FIG. 7 is a diagram explaining 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, and realizes the transfer of heat between the two surfaces as a whole. Therefore, the arrangement density of the semiconductor elements in the Peltier element can be set according to the amount of heat generated by the object to be temperature controlled. Considering the amount of heat generated by each part in 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 is set so that the mounting area of the driver IC > mounting area of the optical modulator chip > mounting area of the spatial optical components.
  • the Peltier element 17 that controls the driver IC should have the highest element density. Furthermore, within the Peltier element 18 that controls the optical modulator chip, the area 18-1 directly below the optical modulator can have a medium density, while the area 18-2 for spatial optical components, etc. can have a low density.
  • the optical transmitter of the present invention can suppress the temperature dependency of the optical modulation output characteristics, and realize an optical transmitter configuration and implementation form with excellent high speed performance.
  • This invention can be used in optical communication networks.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Thermal Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
PCT/JP2022/037031 2022-10-03 2022-10-03 光送信器 Ceased WO2024075168A1 (ja)

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PCT/JP2022/037031 WO2024075168A1 (ja) 2022-10-03 2022-10-03 光送信器
US19/115,384 US20260104602A1 (en) 2022-10-03 2022-10-03 Optical Transmitter

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