JP2010177539A - Transmission light source and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission light source which reduces optical coupling loss between an external resonator having wavelength variable function and a light modulator, and can set waveguide mirror reflectance of the external resonator readily. <P>SOLUTION: A transmission light source 1 has; (i) a wavelength variable filter 131 which can change transmitted light wavelength; (ii) a loop mirror 132 which includes a closed loop-shaped optical waveguide optically connected to one end of the waveguide variable filter 131; (iii) a 2×2 optical coupler 112 which is optically coupled to the loop mirror 132 and can take out part of optical wave propagating through the loop mirror 132 from two ports; (iv) waveguides 106 and 110 which are respectively connected to of the two ports of the optical coupler 112 and work as first and second phase modulators which can modulate a phase of waveguide light; and (v) a 3 dB optical multiplexer 109 which multiplexes output of the waveguides 106 and 110. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light source used for optical communication and optical information processing, and more particularly to a transmission light source including a light source having a wavelength variable function and an optical modulator.

  In recent years, Internet traffic has increased rapidly, and technology for expanding communication capacity has also been developed in response to this. Wavelength division multiplexing (WDM) increases the capacity by increasing the number of wavelengths multiplexed in an optical fiber. With regard to WDM, combined with progress in ROADM (reconfigurable optical add / drop multiplexing), optical cross-connect by wavelength routing, etc., expansion of communication capacity with more flexibility has been actively studied. In this method, wavelength resources are not only used for capacity expansion, but are also actively used for improving network functions. The expansion of communication capacity and the enhancement of the functionality of communication systems are related to each other, and it is possible to provide a low-cost and highly secure communication system. An optical transmitter having a wavelength variable function is This is one of the important devices for constructing a communication system.

  A conventional WDM system uses a plurality of fixed wavelength light sources having a fixed wavelength interval side by side. When a fixed wavelength light source is used, the number of backup light sources for maintenance management increases according to the number of wavelengths used. For this reason, the cost of the backup light source has been a major factor that hinders cost reduction of the system. By applying a wavelength tunable light source, a single backup light source can cope with a plurality of wavelengths, so that the system cost can be greatly reduced. In addition, a wavelength tunable light source having a high switching speed is an indispensable element for realizing a new network function even in wavelength routing.

  A wavelength variable light source capable of covering the C (Conventional) band or the L (Long) band is disclosed in, for example, the following documents. Non-Patent Document 1 discloses a wavelength tunable light source using a movable MEMS (Micro Electro Mechanical Systems) mirror by Jill D. Berger et al. Although the wavelength tunable light source of Non-Patent Document 1 shows relatively good light output characteristics, there are concerns about its practicality in terms of manufacturing cost and impact resistance. Further, a wavelength tunable light source that improves the mode stability of a DBR (Distributed Bragg Reflector) laser and is further integrated with a modulator has been reported in Non-Patent Document 2 by B. Mason et al. There is a problem in terms of sex. On the other hand, a wavelength tunable light source using a planar lightwave circuit (PLC) as an external resonator is relatively easy to manufacture and has no moving parts like MEMS, so that the manufacturing yield and It is excellent in terms of reliability (particularly vibration resistance) and is considered suitable for mass production. Several configurations have been proposed for a wavelength tunable light source using a PLC as an external resonator. For example, a variable wavelength light source configured using a ring resonator and a semiconductor optical amplifier is reported in Non-Patent Document 3 by H. Yamazaki et al. According to the report of Non-Patent Document 3, good characteristics are obtained in terms of wavelength variable range, optical output, and the like.

Jill D. Berger et al., Optical Communication, 2001. ECOC '01. 27th European Conference on, Vol. 2, 30, p.198-199 Mason et al., IEEE Photonics Letters, Vol. 11, NO. 6, 1999, p.638-640 Yamazaki et al., 30th European Conference on Optical Communication 2004, th 4.2.3

  In a wavelength tunable light source using a PLC as an external resonator as disclosed in Non-Patent Document 3, a resonator of the entire element is formed by a ring resonator and a semiconductor optical amplifier. For this reason, in order to further integrate an optical modulator on the same substrate as the ring resonator and the semiconductor optical amplifier, a low loss is maintained between the external resonator and the optical modulator while maintaining the configuration of the external resonator. Need to be optically coupled. That is, there is a need for a new structure that can realize a mirror part having an appropriate reflectivity and can perform optical coupling between the external resonator and the optical modulator part.

  In order to reduce the size of an optical transmitter incorporating a light source having a wavelength variable function and an optical modulator, it is effective to integrate the light source and the optical modulator on the same substrate. A general method of integrating an optical modulator and a wavelength tunable light source having an external resonator and a semiconductor optical amplifier is to place the waveguide end face (mirror surface) of the external resonator close to the waveguide end face of the optical modulator. The optical wave emitted from the mirror surface of the external resonator is optically coupled to the waveguide end face of the optical modulator. In this case, if the end face of the external resonator and the end face of the optical modulator are brought into complete contact, it becomes difficult to set the optical reflectance of the waveguide end face mirror to an optimum value. Therefore, an appropriate gap is required between the waveguide end face of the external resonator and the waveguide end face of the optical modulator. However, if there is an air gap between the waveguides, diffraction loss occurs during light wave propagation, so that the optical coupling between the waveguides cannot be sufficiently reduced. That is, it is not always easy to achieve both reduction in optical coupling loss and optimum setting of the waveguide mirror reflectivity.

  An object of the present invention is to provide a transmission light source capable of reducing the optical coupling loss between an external resonator having a wavelength variable function and an optical modulator and easily setting the waveguide mirror reflectivity of the external resonator.

  The transmission light source according to the first aspect of the present invention includes: (i) a wavelength tunable filter capable of changing a transmitted light wavelength; (ii) a loop mirror including a closed loop optical waveguide; and (iii) one end of the wavelength tunable filter; A multiplexer / demultiplexer for optically connecting the loop mirror; (iV) an optical amplifier optically connected to the other end of the wavelength tunable filter; and (v) an optically coupled to the loop mirror; And (vi) first and second phase modulators connected to the two ports and capable of modulating the phase of the guided light, respectively. And (Vii) a multiplexer for multiplexing the outputs of the first and second phase modulators.

  A transmission light source according to a second aspect of the present invention includes (i) a wavelength tunable filter capable of changing a transmitted light wavelength, and (ii) a closed-loop optical waveguide optically connected to one end of the wavelength tunable filter. A loop mirror; (iii) an optical element optically coupled to the loop mirror and capable of extracting a part of a light wave propagating through the loop mirror from two ports; and (iv) a guide extracted from the two ports. An optical modulator that modulates intensity by phase-modulating wave light and then combining the light is included.

The method for manufacturing a transmission light source according to the third aspect of the present invention includes the following two steps (a) and (b).
(A): (i) a wavelength tunable filter capable of changing the wavelength of transmitted light, (ii) a loop mirror including a closed loop optical waveguide, and (iii) optically connecting one end of the wavelength tunable filter and the loop mirror. A multiplexer / demultiplexer; (iv) an optical element optically coupled to the loop mirror and capable of extracting a part of a light wave propagating through the loop mirror from two ports; (v) extracted from the two ports; Monolithically integrating on the same substrate an optical modulator that modulates the intensity of the guided light after phase modulation, and (b): an optical amplifier is optically connected to the other end of the wavelength tunable filter To connect to.

  According to the present invention, it is possible to provide a transmission light source capable of reducing the optical coupling loss between an external resonator having a wavelength variable function and an optical modulator and easily setting the waveguide mirror reflectivity of the external resonator.

The top view which shows typically the structure of the transmission light source concerning 1st Embodiment. Sectional drawing in the AA of the transmission light source shown in FIG. The top view which shows typically the structure of the transmission light source concerning 2nd Embodiment. Sectional drawing in the BB line of the transmission light source shown in FIG. The top view which shows typically the structure of the transmission light source concerning 3rd Embodiment. The top view which shows typically the structure of the transmission light source concerning 4th Embodiment.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary for the sake of clarity.

<First Embodiment>
FIG. 1 is a schematic plan view showing a schematic configuration of a transmission light source 1 according to the present embodiment. The transmission light source 1 has a wavelength tunable laser and an optical modulator. More specifically, the SOI substrate 101 has a planar structure in which an external resonator 130 and an optical modulator 133 having a wavelength variable function are planarized by an optical waveguide having a silicon layer as a core layer and an upper silicon oxide film as a cladding. It is monolithically integrated as an optical circuit. The external resonator 130 includes a wavelength tunable filter 131 and a loop mirror 132 that can change the transmitted light wavelength. Further, a compound semiconductor optical amplification element (semiconductor optical amplifier (SOA) 116) is mounted on the SOI substrate 101 in a hybrid manner. Details of the transmission light source 1 will be described below.

  On the SOI substrate 101, a first ring type optical waveguide 113 and a second ring type optical waveguide 120 are disposed so as to be optically coupled via a straight waveguide 115. In addition, a linear optical waveguide 114 is arranged in close proximity so as to be optically coupled to the first ring optical waveguide 113. Further, heaters 121 and 122 are arranged above the ring type optical waveguides 113 and 120, respectively. The heaters 121 and 122 can change the resonance condition for the guided light by changing the refractive index of the waveguides 113 and 120 by the thermo-optic effect generated by heating.

  The SOA 116 is disposed so that one end thereof is optically coupled to one end of the linear optical waveguide 114. A high reflection film 117 is laminated on the other end of the SOA 116.

  The linear optical waveguide 102 is disposed close to the waveguide 120 so as to be optically coupled to the second ring optical waveguide 120. One end of the waveguide 102 is connected to a loop mirror 132 including a 3 dB optical demultiplexer 103 and a loop waveguide 104.

  The optical waveguide 123 is disposed so as to be optically close to the loop waveguide 104. Thereby, the directional coupler 112 is configured. Both ends of the optical waveguide 123 are connected to optical waveguides 110 and 106 each having a phase modulation function. The optical waveguides 110 and 106 are connected to the output waveguide 107 via a 3 dB optical multiplexer 109. An antireflection film 108 is disposed on the waveguide end face of the output waveguide 107.

  The optical waveguides 110 and 106, the 3dB optical multiplexer 109, and the output waveguide 107 are Mach-Zehnder interferometers. Further, the optical modulator 133 is configured by arranging the electrodes 105, 111, and 118 for phase modulation. The optical modulator 133 modulates the refractive index of the waveguides 106 and 110 using the carrier plasma effect caused by current injection, thereby performing phase modulation of the guided light.

FIG. 2 shows a cross-sectional structure taken along line AA corresponding to the optical modulator 133 portion. Ridge-type optical waveguides 202 and 205 of non-doped silicon corresponding to the optical waveguides 106 and 110 are formed on the upper portion of the SOI substrate 101 composed of the silicon substrate 207 and the SiO ₂ layer 208 laminated thereon. A clad layer 203 made of a SiO ₂ film is formed on the top. Further, n-type doped silicon layers 206 and 209 and a p-type doped silicon layer 210 are formed on both sides of the ridge type optical waveguides 202 and 205. The n-doped silicon layers 206 and 209 and the p-doped silicon layer 210 together with the optical waveguides 202 and 205 form a pin diode structure in the horizontal direction on the substrate. On top of the doping layers 209, 210 and 206, electrodes 105, 118 and 111 for applying a voltage are stacked. By applying a voltage between the electrodes 105 and 118 or between the electrodes 111 and 118, carriers such as electrons and holes can be generated in the ridge-type optical waveguides 202 and 205, and the refractive index modulation by the carrier plasma effect. Can be applied.

  Hereinafter, the operation mechanism of the transmission light source 1 shown in FIGS. 1 and 2 will be described in detail. As described above, the external resonator 130 includes the tunable filter 131 and the loop mirror 132 including the linear optical waveguides 114, 115, and 102 and the two ring optical waveguides 120 and 113. In such an external resonator 130, only a light wave having a specific wavelength that resonates can reciprocate inside the semiconductor amplifier 116, so that laser oscillation occurs at the specific wavelength that resonates. The resonance wavelength in the external resonator 130 is generated when the resonance wavelengths of the two ring optical waveguides 113 and 120 coincide with each other. By changing the resonance condition of the external resonator 130 by heating with the heaters 121 and 122, the wavelength of laser oscillation can be varied.

  A part of the laser oscillation light wave is guided to the optical waveguides 110 and 106 operating as phase modulators by the directional coupler 112 formed in the loop mirror 132, respectively. In the optical waveguides 110 and 106, phase modulation is added to the guided light by the plasma effect caused by current injection. The phase-modulated light is multiplexed by the 3 dB multiplexer 109 and converted into intensity modulation.

  The transmission light source 1 according to the present embodiment can change the oscillation wavelength of the laser beam to be output by electrical drive control. Furthermore, the transmission light source 1 includes an optical modulator 133 having a function of converting an electric signal into an optical signal, and can be used as, for example, a transmission device for optical communication.

  As described above, in order to integrate the wavelength tunable laser and the optical modulator, it is necessary to achieve both the mirror formation of the laser element portion and the low-loss optical coupling between the wavelength tunable laser and the optical modulator. The transmission light source 1 uses a loop mirror 132 as a mirror of the laser element unit, extracts a part of light by the directional coupler 112, and supplies the extracted light to the optical modulator 133. In this configuration, the mirror loss of the wavelength tunable laser and the optical coupling gain to the optical modulator 133 coincide with each other, so that the fundamental optical loss loss does not occur, and high-efficiency laser oscillation performance is obtained with a low threshold. be able to. The excess loss in the directional coupler 112 becomes an optical coupling loss between the external resonator 130 and the optical modulator 133. This loss should be sufficiently reduced by appropriate design of the directional coupler 112. Is possible. That is, according to the present embodiment, it is possible to obtain a transmission light source in which both the formation of a mirror for laser oscillation and the optical coupling of the external resonator 130 and the optical modulator 133 are compatible.

<Second Embodiment>
In this embodiment, an example of a transmission light source in which not only an external resonator and an optical modulator but also an optical amplifier are monolithically integrated on the same substrate is shown. FIG. 3 is a schematic plan view showing a schematic configuration of the transmission light source 2 according to the present embodiment. The optical amplifier 304, the external resonator 303, and the optical modulator 308 are monolithically integrated on the InP substrate 301. A highly reflective film 305 is disposed on the element end face on the optical amplifier 304 side. On the other hand, an antireflection film 302 is disposed on the end face on the output waveguide 107 side.

  The external resonator 303 includes a variable wavelength filter 309 and a loop mirror 310 that can change the wavelength of transmitted light. The structures of the wavelength tunable filter 309 and the loop mirror 310 are the same as those of the wavelength tunable filter 131 and the loop mirror 132 described above.

  The band gap wavelength of the waveguide core layer constituting the optical amplifier 304 may be set to a shorter wavelength side than the hand gap wavelength of the waveguide core layer of the external resonator 303 and the optical modulator 308 which are other passive optical circuit units. . Thereby, it can suppress that the oscillated laser light wave is largely absorbed by the passive optical circuit part.

  FIG. 4 shows a cross-sectional structure of the optical waveguide taken along line BB corresponding to the optical modulator 308 portion. Optical core layers 405 and 408 are formed on the n-type doped InP substrate 406. The optical core layers 405 and 408 have a multiple quantum well structure in which a plurality of non-doped InGaAsP layers having different compositions and thicknesses are stacked. Further, on the optical core layers 405 and 408, p-type doped InP cladding layers 404 and 409 are stacked. On top of the InP cladding layers 404 and 409, p-type heavily doped InGaAs contact layers 410 and 411 are stacked. Furthermore, electrodes 306 and 307 for injecting current into the core layers 405 and 408 are formed on the InGaAs contact layers 410 and 411, respectively. An electrode 407 is disposed on the back surface of the InP substrate 406 as a counter electrode for the electrodes 306 and 307.

  The operation principle of the transmission light source 2 according to the present embodiment is substantially the same as that of the transmission light source 1 described above, except that a pin structure for injecting current is formed in a direction perpendicular to the substrate. . The transmission light source 2 uses a quantum confined Stark effect generated by applying a reverse bias voltage to the pin waveguide of the optical modulator section (optical modulator 308), thereby enabling high-speed optical modulation. It is superior to the light source 1.

<Third Embodiment>
In the present embodiment, an example of an optical communication light source capable of dynamically adjusting and blocking optical coupling between an external resonator and an optical modulator will be described. In the present embodiment, when changing the oscillation wavelength, it is not necessary to cut off the current injected into the optical amplifier, so the load on the control system can be reduced.

  FIG. 5 is a schematic plan view showing a schematic configuration of the transmission light source 3 according to the present embodiment. A planar optical circuit including an external resonator 504, an optical modulator 503, and a 2 × 2 optical switch 508 is formed on the SOI substrate 509. The resonator 504 including the double ring variable wavelength filter 501 and the loop mirror 502 and the optical modulator 503 are optically coupled via a 2 × 2 optical switch 508. An SOA 510 is disposed at one end of the planar optical circuit so as to be optically coupled to the wavelength tunable filter 501. Further, an antireflection film 506 is disposed at the output end of the planar optical circuit including the external resonator 504 and the like, and a highly reflective film 511 is provided on the end face of the SOA 510.

  The cross-sectional structure of the planar optical circuit including the external resonator 504 and the like is the same as the ridge-type optical waveguide structure described with reference to FIG. 2 in the first embodiment. The structure and operation method of the optical modulator 503 are the same as those of the optical modulator 133 described in the first embodiment.

  The heater 512 is provided above the optical switch 508. The optical switch 508 is activated by heating the waveguide included in the optical switch 508 by the heater 512. Accordingly, for example, light input from the waveguide 513 to the optical switch 508 can be arbitrarily distributed and output between the waveguides 514 and 515. That is, the optical coupling between the loop mirror 502 and the optical modulator 503 can be changed in the range of 0% to 100%. The optical switch 508 may be used to finely adjust the optical output characteristics of the laser or optically separate the resonator 504 and the optical modulator 503 when changing the oscillation wavelength.

<Fourth Embodiment>
In the present embodiment, an optical transmission module provided with a control system for driving a transmission light source will be described. FIG. 6 is a schematic diagram showing the optical transmission module 4 according to the present embodiment. The optical transmission module 4 includes the transmission light source 1 shown in FIG. 1 and its control system. The configuration of the element portion is not limited to the transmission light source 1, and may be the configuration described in other embodiments (for example, the transmission light source 2 or 3).

  In FIG. 6, a drive circuit 602 drives an optical modulator unit included in a transmission light source 601 in which a wavelength variable light source and an optical modulator are integrated. The control circuit 603 controls the tunable filter (specifically, the heaters 121 and 122) and the SOA 116 included in the transmission light source 601. The interface circuit 604 supplies a control signal and a modulation signal to the control circuit 603 and the drive circuit 602, respectively.

  The interface circuit 604 can be mounted inside the module by being mounted on the submount carrier together with the transmission light source 601. Note that the interface circuit 604 may be monolithically integrated as a CMOS circuit on the same SOI substrate as the planar optical circuit included in the transmission light source 1. By integrating the CMOS circuit and the planar optical circuit, it is possible to reduce the size and the mounting cost.

  The transmission light sources 601 included in the transmission light sources 1 to 3 and the module 4 according to the fourth embodiment described in the first to third embodiments efficiently reduce the optical loss between the wavelength tunable laser element and the optical modulator. It is the functional element integrated by the method. For this reason, it is possible to transmit optical signals corresponding to a plurality of wavelengths used in optical communication. By using these transmission light sources 1 to 3 or the module 4, it is possible to integrate the external resonator and the optical modulator necessary for the wavelength tunable laser element with low optical loss. By reducing the optical loss, the optical output during transmission can be increased. In addition, since the current value to be injected into the laser element can be reduced, the power consumption of laser driving can be reduced.

  Further, the transmission light sources 1 to 3 or the module 4 can simultaneously form the optical coupling of the resonator mirror and the optical modulator necessary for the wavelength tunable laser element. For this reason, since the manufacturing process can be simplified and the yield can be improved, the manufacturing cost can be reduced.

  In addition, the transmission light source 1 or 2 that uses a directional coupler for optical coupling between the resonator and the optical modulator, or an optical transmission module including these, can adjust the wavelength by adjusting the coupling length of the directional coupler. The reflectance of the resonator mirror necessary for the variable laser element can be easily changed. That is, optimal adjustment of element performance is easy, and a high-performance element can be realized at low cost.

  In addition, the transmission light source 3 that uses an optical switch for optical coupling between the resonator and the optical modulator or an optical transmission module including the transmission light source 3 uses the optical switch to change the reflectance of the resonator mirror necessary for the wavelength tunable laser element. Can be changed. As a result, the optical modulator and the laser can be optically separated when changing the oscillation wavelength or as required. Further, the optical coupling between the optical modulator and the laser can be arbitrarily adjusted. That is, operations such as dynamic adjustment of element performance and temporary blocking of modulated light are facilitated, and control load can be reduced and reliability can be improved.

  Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention described above.

1, 2, 3 Transmission light source 4 Optical transmission module 101 SOI (Silicon on insulator) substrate 102 Linear optical waveguide 103 3 dB optical demultiplexer 104 Loop optical waveguide 105 Electrode 106 Phase modulation optical waveguide 107 Output optical waveguide 108 Reflection Prevention film 109 3 dB optical multiplexer 110 Phase modulation optical waveguide 111 Electrode 112 Directional coupler 113 First ring optical waveguide 114 Linear optical waveguide 115 Linear optical waveguide 116 Semiconductor optical amplifier (SOA: Semiconductor Optical Amplifier)
117 High reflective film 118 Electrode 120 Second ring type optical waveguide 121 Heater 122 Heater 130 External resonator 131 Tunable filter 132 Loop mirror 133 Optical modulator 202 Ridge type optical waveguide 203 SiO ₂ cladding layer 205 Ridge type optical waveguide 206 n Doped silicon layer 207 silicon substrate 208 SiO ₂ layer 209 n doped silicon layer 210 p doped silicon layer 301 InP substrate 302 antireflection film 303 external resonator 304 semiconductor amplifier 305 high reflection film 306 electrode 307 electrode 308 optical modulator 309 Tunable wavelength filter 310 Loop mirror 402 SiO ₂ cladding layer 404 p-doped InP cladding layer 405 Non-doped multiple quantum well layer (optical core layer)
406 n-doped InP substrate 407 back electrode 408 non-doped multiple quantum well layer (optical core layer)
409 p-doped InP cladding layer 410 InGaAs contact layer 411 InGaAs contact layer 501 Tunable filter 502 Loop mirror 503 Optical modulator 504 External resonator 506 Antireflection film 507 Electrode 508 Optical switch 512 Heater 509 SOI substrate 510 Semiconductor optical amplifier 511 High reflection Film 601 Transmission light source element 602 Optical modulator drive circuit 603 Wavelength variable laser control circuit 604 Interface circuit

Claims (19)

A tunable filter capable of changing the transmitted light wavelength;
A loop mirror including a closed loop optical waveguide;
A multiplexer / demultiplexer that optically connects one end of the wavelength tunable filter and the loop mirror;
An optical amplifier optically connected to the other end of the wavelength tunable filter;
An optical element optically coupled to the loop mirror and capable of extracting a part of a light wave propagating through the loop mirror from two ports;
First and second phase modulators, each connected to the two ports and capable of modulating the phase of the guided light;
A multiplexer for multiplexing the outputs of the first and second phase modulators;
A transmission light source comprising:   The transmission light source according to claim 1, wherein the multiplexer converts the phase modulation by the first and second phase modulators into intensity modulation. The optical element includes an opposing waveguide disposed in proximity to the closed-loop optical waveguide,
3. The transmission light source according to claim 1, wherein a 2 × 2 optical coupler is formed by a portion of the closed-loop optical waveguide that is close to the opposing waveguide and the opposing waveguide. The optical element includes a 2 × 2 optical switch in which two ports are connected to the closed-loop optical waveguide and the other two ports are connected to the first and second phase modulators,
Furthermore, the said optical switch is a transmission light source of Claim 1 or 2 which can change dynamically the ratio of the light wave power taken out from the said loop mirror.   The transmission light source according to claim 4, wherein the optical switch is a Mach-Zehnder type. The wavelength tunable filter is
A plurality of ring-shaped optical waveguides connected in cascade;
Means for changing a resonance wavelength by changing a refractive index of at least a part of the plurality of ring optical waveguides;
The transmission light source according to claim 1, comprising:   7. The tunable filter, the loop mirror, the multiplexer / demultiplexer, the optical element, and the phase modulator are monolithically integrated on the same substrate. The transmission light source described in 1. The optical amplifier includes an optical amplifier composed of a compound semiconductor,
The wavelength tunable filter, the loop mirror, the multiplexer / demultiplexer, the optical element, and the phase modulator are formed by a silicon waveguide made from an SOI (Silicon on Insulator) substrate. The transmission light source described. The optical amplifier includes an optical amplifier composed of a compound semiconductor,
The optical switch, the wavelength tunable filter, the loop mirror, the multiplexer / demultiplexer, the optical element, and the phase modulator include a silicon waveguide formed from an SOI (Silicon on Insulator) substrate,
5. The transmission light source according to claim 4, wherein the optical switch performs phase modulation by a thermo-optic effect due to heating of the waveguide by a heater or a carrier plasma effect generated by current injection into the waveguide.   The first and second phase modulators include a silicon waveguide made from an SOI (Silicon on Insulator) substrate, and are generated by a thermo-optic effect caused by heating of the waveguide by a heater or current injection into the waveguide. The transmission light source according to claim 8 or 9, wherein phase modulation is performed by a carrier plasma effect. The optical amplifier, the wavelength tunable filter, the loop mirror, the multiplexer / demultiplexer, the optical element, and the optical waveguide constituting the phase modulator are monolithically integrated on the same compound semiconductor substrate,
The resonant wavelength of the wavelength tunable filter and the phases of the first and second phase modulators are changed by changing the refractive index of the waveguide by an electro-optic effect generated by current injection or voltage application into the waveguide. The transmission light source according to claim 6.   The energy band gap wavelength of the core layer of the optical waveguide formed on the compound semiconductor is set closer to the shorter wavelength side than the optical amplifier in the wavelength tunable filter and the first and second phase modulator sections. The transmission light source according to claim 11.   The transmission light source according to claim 1, further comprising a control circuit for controlling a resonance wavelength of the wavelength tunable filter and a drive circuit for driving the first and second phase modulators.   A control circuit for controlling a resonance wavelength of the wavelength tunable filter, a control circuit for controlling the optical switch, and a drive circuit for driving the first and second phase modulator units. Item 5. The transmission light source according to Item 4. A tunable filter capable of changing the transmitted light wavelength;
A loop mirror including a closed loop optical waveguide optically connected to one end of the wavelength tunable filter;
An optical element optically coupled to the loop mirror and capable of extracting a part of a light wave propagating through the loop mirror from two ports;
An optical modulator that performs intensity modulation by phase-modulating the guided light extracted from the two ports and then multiplexing the waveguide light;
A transmission light source comprising: The optical element includes an opposing waveguide disposed in proximity to the closed-loop optical waveguide,
The transmission light source according to claim 15, wherein a 2 × 2 optical coupler is formed by a portion of the closed-loop optical waveguide adjacent to the opposing waveguide and the opposing waveguide. The optical element includes a 2 × 2 optical switch in which two ports are connected to the closed-loop optical waveguide, and the other two ports are connected to the optical modulator,
Furthermore, the said optical switch is a transmission light source of Claim 15 which can change dynamically the ratio of the light wave power taken out from the said loop mirror. (I) a wavelength tunable filter capable of changing a transmitted light wavelength, (ii) a loop mirror including a closed loop optical waveguide, and (iii) an optical multiplexer / demultiplexer optically connecting one end of the wavelength tunable filter and the loop mirror. (Iv) an optical element optically coupled to the loop mirror and capable of extracting a part of a light wave propagating through the loop mirror from two ports; (v) guided light extracted from the two ports; Monolithically integrating an optical modulator that performs intensity modulation by combining after phase modulation, and optically connecting an optical amplifier to the other end of the wavelength tunable filter;
A method of manufacturing a transmission light source including:   The method of claim 18, further comprising monolithically integrating the optical amplifier on the substrate.

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