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US-20260128798-A1 - Optical Transmitter

US20260128798A1US 20260128798 A1US20260128798 A1US 20260128798A1US-20260128798-A1

Abstract

There is provided a novel configuration and mounting form of an optical transmitter that suppresses temperature dependency of optical modulation output characteristics and has excellent speed. An optical transmitter according to the present disclosure includes an optical modulator chip, a driver IC for operating the optical modulator chip, a wiring layer that guides a modulated electrical signal supplied from an external digital signal processor (DSP) to the driver IC, a gold wire line that connects each of the driver IC and the optical modulator chip, and the wiring layer and the driver IC via a PAD, and a Peltier device mounted below the optical modulator chip and the driver IC, in which the optical modulator chip and the driver IC are temperature-controlled by the Peltier device that is the same.

Inventors

  • Josuke Ozaki
  • Yoshihiro Ogiso
  • Mitsuteru Ishikawa

Assignees

  • NIPPON TELEGRAPH AND TELEPHONE CORPORATION

Dates

Publication Date
20260507
Application Date
20221003

Claims (10)

  1. 1 . An optical transmitter comprising: an optical modulator chip; a driver IC for operating the optical modulator chip; a wiring layer that guides a modulated electrical signal supplied from an external digital signal processor (DSP) to the driver IC; a gold wire line that connects each of the driver IC and the optical modulator chip, and the wiring layer and the driver IC via a PAD; and a Peltier device mounted below the optical modulator chip and the driver IC, wherein the optical modulator chip and the driver IC are temperature-controlled by the Peltier device that is the same.
  2. 2 . The optical transmitter according to claim 1 , wherein the gold wire line is a ball wire having a loop, a height difference between an upper surface of the optical modulator and an upper surface of the driver IC is equal to or less than 100 μm, a height difference between an upper surface of the wiring layer and an upper surface of the driver IC is equal to or less than 100 μm, and in the driver IC and the PAD installed in the optical modulator chip, at least two or more of the gold wire lines are connected between signal PADs that signals are propagated.
  3. 3 . The optical transmitter according to claim 1 , wherein the gold wire line is a ribbon wire having a planar shape, and heights of an upper surface of the optical modulator, an upper surface of the driver IC, and an upper surface of the wiring layer coincide with each other.
  4. 4 . The optical transmitter according to claim 2 , wherein a distance between the optical modulator and the driver IC is 50 μm or less, and the PAD that the gold wire line is connected is formed at a position within 50 μm from a chip end surface of the optical modulator or the driver IC.
  5. 5 . The optical transmitter according to claim 1 , wherein the temperature of the Peltier device is controlled to be constant at any temperature in a range of 25 to 50° C.
  6. 6 . The optical transmitter according to claim 1 , wherein a material of an upper surface of the Peltier device is aluminum nitride (AlN), the optical modulator chip is an indium phosphide (InP) optical modulator chip, and the Peltier device is connected to the optical modulator chip and the driver IC by a conductive paste or solder having a thermal conductivity of 30 W/m K or more.
  7. 7 . The optical transmitter according to claim 1 , further comprising: an optical member that temperature is controlled by the Peltier device, wherein element densities of n-type and p-type semiconductors constituting the Peltier device are set such that an area that the driver IC is mounted, an area that the optical modulator chip is mounted, a mounting area of the optical member are in descent order.
  8. 8 . The optical transmitter according to claim 1 , further comprising a subcarrier between the Peltier device and the optical modulator chip and the driver IC.
  9. 9 . The optical transmitter according to claim 7 , further comprising a thermal separation groove on at least one of an upper surface or a lower surface of the subcarrier between the driver IC and the optical modulator chip.
  10. 10 . The optical transmitter according to claim 1 , wherein the optical modulator chip and the driver IC are mounted in a housing in a HB-CDM form, and the optical modulator chip and the driver IC have a differential line configuration.

Description

TECHNICAL FIELD The present disclosure relates to an optical transmitter used in optical communication. More particularly, the present disclosure relates to a mounting form of an optical transmitter including a semiconductor optical modulator and a driver IC thereof. BACKGROUND ART In order to respond to a rapid traffic increase of a communication network, digital coherent optical transmission combining a coherent communication method and a digital signal processing technology has been introduced into an optical fiber communication system. Starting from the establishment of a backbone network transmission technology of 100 Gbps per wavelength at the beginning, transmission of 400 to 600 Gbps per wavelength, which is faster, has been put into practical use at present. In the above-described digital coherent optical transmission, an optical transmission-reception device in which an optical receiver and an optical transmitter are integrated is used. In an optical transmission-reception device of a system having a transmission capacity exceeding 400 Gbps, an analog component such as a high frequency (RF) electric circuit is required to have a wider bandwidth, and for example, in an optical modulator, a modulation bandwidth of 40 GHz or more is necessary. For reduction of high frequency loss and downsizing of a device, which are linked to a wider bandwidth, for example, a form in which an RF driver IC and an optical modulator are mounted in an integrated package on the transmission side has attracted attention. A mounting form of the optical transmitter is also standardized by the Optical Internetworking Forum (OIF) under the name of High-Bandwidth Coherent Driver Modulator (HB-CDM) (Non Patent Literature 1). Also on the reception side of the optical transmission-reception device, a transimpedance amplifier (TIA) and an optical receiver are mounted in an integrated package, and is also referred to as an integrated coherent receiver (ICR). Turning to materials for optical transmitting and receiving devices, semiconductor-based optical modulators have attracted attention instead of conventional lithium niobate (LN) optical modulators from the viewpoint of miniaturization and cost reduction. For higher-speed modulation operation, a compound semiconductor represented by InP is mainly used. In addition, research and development are concentrated on Si-based optical devices in systems in which more miniaturization and cost reduction are regarded as important. There are advantages and disadvantages inherent to the materials also in the above-described semiconductor optical modulator, and for example, in an InP optical modulator, temperature control of an optical modulator chip is essential during operation in order to control a band edge absorption effect. On the other hand, the Si optical modulator has a merit that temperature control is unnecessary, but has a smaller electro-optical effect than other material systems. For this reason, it is necessary to increase the electro-optical interaction length, and as a result of increasing the device length, a high frequency loss may be increased. There are many problems in further increasing the speed and bandwidth of the optical modulator including a mounting technology for increasing the bandwidth and reducing the size. The operation temperature (case temperature) of the optical transmitter based on the HB-CDM is required to be in a range of at least −5° C. to 75° C. In order to ensure such an operation temperature, generally, only an optical modulator chip is mounted on a Peltier device in consideration of power consumption (Patent Literature 1). However, in the optical transmitter of the related art, deterioration of high frequency characteristics of the driver IC at high temperature has been a problem. Specifically, in a case where the environmental temperature is in a high temperature state, there has been a problem that the high frequency band, the peaking amount, and the gain of the driver IC are deteriorated. As optical transmitters have increased in speed and bandwidth, the influence of deterioration in signal quality due to the above-described deterioration cannot be ignored. Thus, an optical transmitter capable of maintaining a constant high frequency characteristic regardless of a change in environmental temperature is desired. CITATION LIST Patent Literature Patent Literature 1: WO 2021/171599 A1 Non Patent Literature Non Patent Literature 1: OIF, Implementation Agreement for the High Bandwidth Coherent Driver Modulator (HB-CDM), [online], Jul. 15, 2021, [Searched on Sep. 1, 2022], the Internet <URL: https://www.oiforum.com/wp-content/uploads/OIF-HB-CDM-02.0.pdf>Non Patent Literature 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, Sep. 15, 2020, doi: 10.1109/JLT.2020.2998466. SUMMARY OF INVENTION In