JP2007115900A - Wavelength tunable light source, module thereof, and method for driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength tunable light source with a larger wavelength tunable range. <P>SOLUTION: The wavelength tunable light source is constituted of a tunable filter for varying the wavelength of a spectrum peak of intensity transmittance and a plurality of semiconductor amplifiers optically coupled with the filter and having different wavelength regions of a gain spectrum. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light source used for optical communication, optical information processing, optical interconnection, and the like, and more particularly to a wavelength tunable light source having a wavelength tunable function, a driving method thereof, and a wavelength tunable light source module.

  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) is intended to increase the capacity by increasing the number of wavelengths. Therefore, expansion of communication capacity with more flexibility is being 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 service, and the wavelength tunable laser constructs such a communication system. It is one of the key devices important above.

  In conventional wavelength division multiplexing systems, a plurality of fixed wavelength light sources having a fixed wavelength interval are arranged side by side, and the cost of maintenance management backup light sources (for the number of wavelengths) is particularly large, which hinders cost reduction of the system. It was a factor. By applying the wavelength tunable light source, the types of light sources can be integrated into one, which greatly reduces the system cost. 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.

  As a variable wavelength light source capable of covering the C (Conventional) band or the L (Long) band, it is assumed that a movable MEMS mirror is used. Non-Patent Document 1 is published by Berger et al. Although the wavelength tunable light source disclosed in this document shows relatively good light output characteristics, there is concern about its practicality in terms of manufacturing cost and impact resistance. Further, the mode stability of a DBR (Distributed Bragg Reflector) laser is improved and further integrated with a modulator. Although reported in Non-Patent Document 2 by Mason et al., There are problems in terms of cost reduction and reliability.

On the other hand, a wavelength tunable light source using a planar optical circuit (PLC) as an external resonator is not only relatively easy to manufacture, but also has no movable part as in a MEMS. Therefore, it is excellent in terms of production yield and reliability (particularly vibration resistance) and is considered suitable for mass production, and several configurations have been proposed at present. As a configuration using a ring-type external resonator and a semiconductor amplifier, H.K. Reported in Non-Patent Document 3 by Yamazaki et al. According to the report of this document, as a wavelength tunable light source having no movable part, good characteristics are obtained in terms of a wavelength tunable range, light output, and the like.
Optical Communication, 2001. ECOC'01.27th European Conference on Volume 2,30 P.E. 198-199 IEEE Photonics Letters Volume 11 Number 11, 1999 P.I. 638-640 30th European Conference on Optical Communication 2004, th4.2.3

  However, in the wavelength tunable light source having the configuration proposed in Non-Patent Document 3, the wavelength tunable range of the output light is determined by the wavelength tunable range of the ring-type external resonator and the wavelength amplification range of the semiconductor amplifier. Therefore, there is a structural limit to make the wavelength variable in a stable and wider range.

  On the other hand, in a high-density wavelength division multiplex transmission system (DWDM) in optical communication, a communication wavelength band is divided into a C band and an L band, and a large number of wavelength signal lights are introduced in a wavelength range of about 40 nm. Currently, many tunable lasers are being developed based on a wavelength range of 40 nm. However, it is not a communication wavelength band that can cover both the C and L bands with a single light source. Further, in the CWDM (Coarse WDM) system in which the signal light wavelength is set at intervals of about 20 nm, a wider range of wavelength variation is required.

  The present invention has been made to solve the above-described problems of the prior art, and provides a wavelength tunable light source, a wavelength tunable light source module, and a wavelength tunable light source driving method having a larger wavelength tunable range. The purpose is to do.

In order to achieve the above object, the wavelength tunable light source of the present invention comprises:
A wavelength tunable filter for changing the wavelength of the spectral peak of the transmitted light intensity;
A plurality of semiconductor amplifiers optically coupled to the tunable filter and having different gain spectrum wavelength regions;
It is the structure which has.

The wavelength tunable light source of the present invention is
A wavelength tunable filter for changing the wavelength of the spectral peak of the transmitted light intensity;
A semiconductor amplifier optically coupled to the wavelength tunable filter, wherein a plurality of gain media having different wavelength regions of the gain spectrum are disposed along the waveguide direction;
It is the structure which has.

  In the present invention, by changing both the gain spectrum by the plurality of semiconductor amplifiers or the plurality of gain regions and the loss spectrum of the wavelength tunable filter, the selection range of the wavelength of the output light becomes wider.

On the other hand, the tunable light source module of the present invention for achieving the above object is
The wavelength tunable light source of the present invention,
A control circuit for a multiple ring resonator for controlling the multiple ring resonator;
A semiconductor amplifier control circuit for controlling the optical gain of the plurality of semiconductor amplifiers;
It is the structure which has.

The wavelength tunable light source module of the present invention is
The wavelength tunable light source of the present invention,
A control circuit for a multiple ring resonator for controlling the multiple ring resonator;
A control circuit for a semiconductor amplifier for controlling an optical gain of a plurality of gain media of the semiconductor amplifier;
It is the structure which has.

Moreover, the driving method of the wavelength tunable light source of the present invention for achieving the above-described object, the wavelength tunable light source of the present invention,
A current is generated so that an optical gain necessary for spectrum generation is generated in a predetermined semiconductor amplifier among the plurality of semiconductor amplifiers corresponding to a desired wavelength, and an optical loss is not generated in the semiconductor amplifiers other than the predetermined semiconductor amplifier. Performing injection and operating the predetermined semiconductor amplifier in gain;
The oscillation wavelength of the wavelength tunable filter is adjusted corresponding to the desired wavelength.

Furthermore, the wavelength tunable light source driving method of the present invention is the above tunable light source of the present invention.
A current is generated so that an optical gain necessary for generating a spectrum is generated in a predetermined gain medium among the plurality of gain media corresponding to a desired wavelength, and an optical loss is not generated in gain media excluding the predetermined gain medium. Performing the injection to gain operation of the predetermined gain medium;
The oscillation wavelength of the wavelength tunable filter is adjusted corresponding to the desired wavelength.

  According to the present invention, both the wavelength tunable filter capable of changing the peak position of the loss spectrum within a predetermined range and the gain variable medium capable of greatly changing the gain spectrum shape, in particular, the peak position of the gain spectrum, have the oscillation wavelength. Since it can be used for control, a wider range of wavelength tunability can be realized for the output light.

  The wavelength variable light source of the present invention is characterized in that a configuration having a plurality of gain spectra in different wavelength regions is optically coupled to a wavelength variable filter. In the following description, the wavelength tunable light source is a laser.

(First embodiment)
The configuration of the wavelength tunable laser according to the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration example of a wavelength tunable laser according to the present embodiment.

  As shown in FIG. 1, the wavelength tunable laser includes a wavelength tunable external resonator formed by a planar optical circuit 1 formed on a quartz-based material substrate, a first semiconductor amplifier 11 provided on the end face 12 side of the substrate, The second semiconductor amplifier 4 is provided on the end face 6 side.

  The wavelength tunable external resonator of the planar optical circuit 1 includes a linear optical waveguide 8, a first ring optical waveguide 7 partially optically coupled to the linear optical waveguide 8 with an appropriate degree of coupling KL, and a first ring type. A linear optical waveguide 13 partially optically coupled to the optical waveguide 7 with a coupling degree KL, a second ring optical waveguide 14 partially optically coupled to the linear optical waveguide 13 with a coupling degree KL, and a second ring type In this configuration, the optical waveguide 14 and the linear optical waveguide 2 partially optically coupled with a coupling degree KL are formed on the same plane. This wavelength tunable external resonator becomes a multiple ring resonator having the plurality of ring waveguides. One end of the straight optical waveguide 8 terminates at the end face 12 of the substrate, and one end of the straight optical waveguide 2 terminates at the end face 6 of the substrate. Low reflection films 27 and 26 for suppressing optical reflection are formed on the end faces 12 and 6, respectively.

  The first semiconductor amplifier 11 has a band gap that generates a gain spectrum in a predetermined wavelength region. The second semiconductor amplifier 4 has a band gap that generates a gain spectrum in a region having a longer wavelength than the gain spectrum generated by the first semiconductor amplifier 11. In the first semiconductor amplifier 11, a low reflection film 29 is formed on the end face on the substrate side, and an optical thin film 37 is formed on the end face 10 on the opposite side to obtain a reflectivity of about 10%. In the second semiconductor amplifier 4, a low reflection film 28 is formed on the end face on the substrate side, and an optical thin film 38 is formed on the end face 5 on the opposite side so as to obtain a high reflectivity of 90% or more.

  The reflectivity of the optical thin film 37 may be about 5%, but it is more preferably about 10% as the reflectivity capable of causing oscillation in the resonator and outputting the laser to the outside. The optical thin film 38 preferably has a reflectivity of at least 70% in order to cause laser oscillation in the resonator.

  One end of the linear optical waveguide 8 is optically coupled to the low reflection output waveguide end 9 by the low reflection film 29 of the first semiconductor amplifier 11 at the end face 12 of the substrate. One end of the linear optical waveguide 2 is optically coupled to the low reflection output waveguide end 3 by the low reflection film 28 of the second semiconductor amplifier 4 at the end face 6 of the substrate. For the sake of explanation, FIG. 1 shows a state in which the first semiconductor amplifier 11 and the substrate are arranged apart from each other. Further, it is desirable that the low reflection films 26 to 29 have a reflectance close to 0%.

  Further, a heater 15 for heating the core layer of the waveguide and a heat insulating groove 16 for suppressing thermal diffusion are formed in a part of the second ring type optical waveguide 14. The heater 15 is located in a range where the temperature of the core layer of the waveguide can be changed, such as above, below, or beside the waveguide. In FIG. 1, the heater 15 is provided on the waveguide. The first ring-type optical waveguide 7 and the second ring-type optical waveguide 14 have slightly different peripheral lengths and different optical path lengths.

  Here, the operating principle of the wavelength tunable laser of this embodiment will be briefly described.

FIG. 2 is a schematic diagram for explaining the operating principle of the wavelength tunable laser according to the present embodiment. The wavelength tunable laser shown in FIG. 2 is a model for explaining the principle of the wavelength tunable laser of this embodiment. As shown in FIG. 2, the wavelength tunable laser includes a wavelength tunable filter 46 having an FSR (free spectrum range) wavelength λ _FSR and a gain tunable medium 47 capable of changing the gain spectrum in an optically low reflection manner. Are connected. In the wavelength tunable filter 46, a high reflection film 48 having a reflectance higher than a predetermined value is formed on the end face opposite to the end face coupled to the gain variable medium 47. In the variable gain medium 47, a low reflection film 49 having a reflectivity lower than a predetermined value is formed on the end surface opposite to the end surface coupled to the wavelength tunable filter 46.

  When the magnitude of the gain of the variable gain medium 47 becomes larger than the sum of the optical losses at the variable wavelength filter 46, the variable gain medium 47, and the respective reflection end surfaces due to current injection into the variable gain medium 47 or the like, the high reflection film 48 is obtained. To the low reflection film 49 causes laser oscillation due to stimulated emission with a resonator as a resonator. Then, laser light is output from the end face of the low reflection film at one end of the variable gain medium 47. As the wavelength of the oscillated laser beam, a wavelength that is the maximum gain in the sum of the loss spectrum of the wavelength variable filter 46 and the gain spectrum of the gain variable medium 47 is selected.

FIG. 3 is a schematic diagram showing the loss spectrum of the transmitted light intensity of the wavelength tunable filter, and FIG. 4 is a schematic diagram showing the outline of the gain spectrum of the variable gain medium. Since the spectrum of the gain medium is fixed in the conventional wavelength tunable laser, the variable oscillation wavelength range is limited to the FSR (λ _FSR ) of the wavelength tunable filter as shown in FIG. On the other hand, in the wavelength tunable laser shown in FIG. 2, the wavelength tunable range can be greatly expanded beyond the FSR of the wavelength tunable filter by changing the spectrum of the gain medium as shown in FIG. It becomes. The dashed-dotted line shown in the graph of FIG. 4 is the case where the peak position of the gain spectrum is on the long wavelength side, the broken line is the case where the peak position is on the short wavelength side, and the solid line is the peak position near the middle of them. Is the case.

  The wavelength tunable external resonator of the wavelength tunable laser of this embodiment shown in FIG. 1 corresponds to the wavelength tunable filter 46 shown in FIG. 2, and the first semiconductor amplifier 11 and the second semiconductor amplifier 4 are shown in FIG. This corresponds to a variable gain medium. Based on this principle, the operation of the wavelength tunable laser of this embodiment shown in FIG. 1 will be described below.

  When current is injected into the first semiconductor amplifier 11 and the second semiconductor amplifier 4, a part of the excitation light is a straight optical waveguide 8, a first ring optical waveguide 7, a linear optical waveguide 13, and a second ring type. It propagates in the order of the optical waveguide 14 and the linear optical waveguide 2, or propagates in the reverse order. Then, the second semiconductor amplifier 4 and the first semiconductor amplifier 11 induce stimulated emission to increase the number of photons. Part of the induced photon propagates back and forth in the planar optical circuit 1 with the first semiconductor amplifier 11 and the second semiconductor amplifier 4 again at the end face 10 or the end face 5. Laser oscillation occurs when the rate of increase in the number of photons due to stimulated emission is larger than the rate of decrease in the number of photons due to propagation loss inside the semiconductor amplifier and the planar circuit and the mirror loss at the end surfaces 10 and 5. Laser light is emitted.

  FIG. 5 is a schematic diagram showing a loss spectrum of a light wave output incident from the end face of the linear optical waveguide 2 having the end face 6 as one end and emitted from the end face of the linear optical waveguide 8 facing the end face 12 in the planar optical circuit 1. It is.

  As shown in FIG. 5, due to the overlap of transmission characteristics of two different ring-type optical waveguides, in addition to a sharp short period loss, a gentle long period characteristic is superimposed. The wavelength interval from the loss peak 31 to the loss peak 32 is the FSR 33 of the planar circuit 1. Due to the thermo-optic effect caused by the heating of the heater 15, the refractive index fluctuation of the waveguide occurs, the resonance wavelength of the wavelength tunable external resonator changes, and the loss peak shifts along the wavelength axis. When this shift amount reaches FSR, the same spectrum shape appears again. That is, the maximum peak shift amount by the heater 15 is equal to the FSR 33.

  Next, operating conditions of the first semiconductor amplifier 11 and the second semiconductor amplifier 4 will be described.

  FIG. 6 is a diagram showing a case where a large gain spectrum is generated on the short wavelength side. A large gain is generated in the first semiconductor amplifier 11 and a small gain is generated in the second semiconductor amplifier 4 to compensate for the loss. As a result, as shown in FIG. 6, the gain spectrum 22 on the long wavelength side by the second semiconductor amplifier 4 is smaller than the laser oscillation level, but the gain spectrum 23 on the short wavelength side by the first semiconductor amplifier 11 is laser oscillation. Over the level. In this case, the wavelength region 24 becomes a laser oscillation possible region. Under the operating conditions shown in FIG. 6, laser oscillation occurs at the wavelength of the loss peak 31 shown in FIG. 5, and the wavelength can be varied in the wavelength region 34 by the heater 15.

  FIG. 7 is a diagram showing a case where a large gain spectrum is generated on the long wavelength side. A large gain is generated in the second semiconductor amplifier 4 and a small gain is generated in the first semiconductor amplifier 11 to compensate for the loss. As a result, as shown in FIG. 7, the gain spectrum 42 on the short wavelength side by the first semiconductor amplifier 11 is smaller than the laser oscillation level, but the gain spectrum 43 on the long wavelength side by the second semiconductor amplifier 4 is laser oscillation. Over the level. In this case, the wavelength region 44 becomes a laser oscillation possible region. 7, laser oscillation occurs at the wavelength of the loss peak 32 shown in FIG. 5, and the wavelength can be varied in the wavelength region 35 by the heater 15.

  The wavelength tunable laser of this embodiment covers the wavelength range of the short wavelength side wavelength region 34 and the long wavelength side wavelength region 35 shown in FIG. 5 by controlling the heater on the ring optical waveguide and the two semiconductor amplifiers. Can do.

  In the present invention, the selection range of the wavelength of light to be output becomes wider by changing both the gain spectrum by the gain variable medium of the plurality of semiconductor amplifiers or the plurality of gain regions and the loss spectrum of the wavelength tunable filter. This is because both the tunable filter that can change the peak position of the loss spectrum within a predetermined range and the variable gain medium that can greatly change the gain spectrum shape, especially the peak position of the gain spectrum, are used to control the oscillation wavelength. This is because a wider range of wavelength tunability can be realized for the output light.

  In addition, a variable wavelength external resonator capable of controlling the oscillation wavelength with a small amount but a high accuracy is used as a fine adjustment of the wavelength. On the other hand, a plurality of semiconductor amplifiers cannot be controlled with a high degree of accuracy. As a rough adjustment of the wavelength. For this reason, the wavelength tunable range is larger than that in the prior art, and highly accurate wavelength tunable operation is possible.

(Second Embodiment)
The wavelength tunable laser according to this embodiment is a combination of a gain functional element monolithically integrated with two gain media each having a gain spectrum in a different wavelength region and a double ring resonator.

  The configuration of the wavelength tunable laser according to this embodiment will be described. In addition, about the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted.

  FIG. 8 is a schematic diagram showing a configuration example of the wavelength tunable laser according to the present embodiment. The wavelength tunable laser has a configuration including a wavelength tunable external resonator formed by a planar optical circuit 1 formed on a quartz-based material substrate and a semiconductor amplifier 101 provided on the end face 12 side of the substrate.

  As shown in FIG. 8, the variable wavelength external resonator of the planar optical circuit 1 includes a straight optical waveguide 8, a first ring optical waveguide 7, a linear optical waveguide 13, and a second ring optical waveguide 14. The linear optical waveguide 2 is formed on the same plane. This wavelength tunable external resonator becomes a multiple ring resonator having the plurality of ring waveguides. One end of the linear optical waveguide 8 terminates at the end surface 12 of the substrate, and one end of the linear optical waveguide 2 terminates at the end surface 17 of the substrate. A low reflection film 27 for suppressing optical reflection is formed on the end face 12, and a high reflection film 70 for obtaining 90% or more optical reflection is formed on the end face 17.

  The semiconductor amplifier 101 includes a short wave gain region 102 of a gain medium having a short wave side gain spectrum which is a short wavelength side, and a long wave gain region 103 of a gain medium having a long wave side gain spectrum which is a long wavelength side. It is a configuration. The short wave gain region 102 and the long wave gain region 103 are optically coupled. In the short wave gain region 102, an optical thin film 72 for obtaining a reflectance of about 10% is formed on the end surface 71 opposite to the end surface optically coupled to the long wave gain region 103. A low reflection film 29 is formed on the end face 12 side of the substrate in the long wave gain region 103. One end of the linear optical waveguide 8 is optically coupled to the low reflection output waveguide end 9 by the low reflection film 29 in the long wave gain region 103 of the semiconductor amplifier 11 at the end face 12 of the substrate. Although not shown in the drawing, each of the short wave gain region 102 and the long wave gain region 103 is provided with an electrode for injecting a current to generate a gain.

  Next, the operation of the wavelength tunable laser of this embodiment will be described.

  When current is injected into the short wave gain region 102 and the long wave gain region 103 of the semiconductor amplifier 101, a part of the excitation light is a straight optical waveguide 8, a first ring optical waveguide 7, a linear optical waveguide 13, a second ring type. The light propagates in the order of the optical waveguide 14 and the straight optical waveguide 2. Then, the light is reflected by the highly reflective end face 17 and returns to the semiconductor amplifier 101 again to induce stimulated emission to increase the number of photons. Some of the induced photons are reflected by the end face 71 of the semiconductor amplifier 101 and input to the planar optical circuit 1 again. Thereafter, it propagates in the semiconductor amplifier 101 and the planar optical circuit 1 in a round-trip manner. Laser oscillation occurs when the rate of increase in the number of photons due to stimulated emission is greater than the rate of decrease in the number of photons due to the propagation loss inside the semiconductor amplifier 101 and the planar circuit and the mirror loss at the reflection end face. Laser light is emitted from the end face 71.

  In the wavelength tunable laser according to the present embodiment, since the semiconductor amplifier is formed as one element, there is only one optical coupling portion between the planar circuit 1 and the semiconductor amplifier 101. Therefore, it is possible to reduce the coupling loss and the optical adjustment load at the time of assembling the module, thereby improving the optical output and reducing the assembling cost.

  In addition, the wavelength tunable laser according to the present embodiment has a simple configuration in which a plurality of gain media having different gain spectra are optically cascaded as a gain variable medium used as a coarse wavelength adjustment function. Furthermore, it is sufficient to give sufficient gain to one of a plurality of gain media necessary for oscillation, and the other gain media may be operated to such an extent that the gain medium itself does not cause an optical loss. The configuration is simple and the control is not complicated.

(Third embodiment)
The wavelength tunable laser of this embodiment is obtained by monolithically integrating two gain media having a gain spectrum in different wavelength regions and a double ring resonator on the same semiconductor substrate.

  FIG. 9 is a schematic diagram showing a configuration example of the wavelength tunable laser according to the present embodiment. The wavelength tunable laser has a configuration including a wavelength tunable external resonator using a planar optical circuit 51 formed on a substrate made of a semiconductor material, and a semiconductor amplifier 501 provided on the substrate.

  As shown in FIG. 9, the variable wavelength external resonator of the planar optical circuit 51 includes a linear optical waveguide 57 and a first ring optical waveguide 55 partially optically coupled to the linear waveguide 57 with an appropriate degree of coupling KL. A linear optical waveguide 56 partially optically coupled to the first ring optical waveguide 55 with a coupling degree KL, and a second ring optical waveguide 52 partially optically coupled to the linear optical waveguide 56 with a coupling degree KL. And the second ring-type optical waveguide 52 and the linear optical waveguide 53 partially optically coupled with the degree of coupling KL are formed in a state having a PIN junction on the same plane.

  The semiconductor amplifier 501 includes a short wave gain region 59 of a gain medium having a short wave side gain spectrum and a long wave gain region 58 of a gain medium having a long wave side gain spectrum. Wirings (not shown) for injecting current into the short wave gain region 59 and the long wave gain region 58 are provided separately.

  One end of the linear optical waveguide 53 terminates at an end face 54 of the substrate, and a high reflection film 63 for obtaining 90% or more of optical reflection is formed on the end face 54. One end of the linear optical waveguide 57 is continuously optically coupled to the semiconductor amplifier 501. In the semiconductor amplifier 501, an optical thin film 65 for obtaining a reflectivity of about 10% is formed on the end surface opposite to the end surface optically coupled to the linear optical waveguide 57. The end face on which the optical thin film 65 is formed is a part of the end face 64 of the substrate.

  A PIN (P-Intrinsic-N) junction 61 for applying an electric field to the core layer of the waveguide is formed in a part of the second ring type optical waveguide 52. By applying an electric field to the core layer of the waveguide of the ring resonator, the refractive index of the core layer is changed by the electro-optic effect by applying the electric field, thereby changing the resonance wavelength of the wavelength tunable external resonator. By using a PIN junction structure as an electrode for applying an electric field to the core layer, the response speed of the change in resonance wavelength to the application of the electric field becomes faster. Further, the peripheral lengths of the first ring-type optical waveguide 55 and the second ring-type optical waveguide 52 are slightly different.

  In the wavelength tunable external resonator, a plurality of ring optical waveguides and a plurality of linear optical waveguides are monolithically integrated on a semiconductor substrate, so that a band gap exists in the core layer of the semiconductor optical waveguide. If the wavelength of light that serves as a reference for whether energy of input light is absorbed is referred to as a band gap wavelength, light having a wavelength longer than the band gap wavelength is not absorbed. Therefore, in order not to cause energy loss in the wavelength tunable external resonator, it is desirable that the light input from the semiconductor amplifier 501 to the wavelength tunable external resonator has a wavelength longer than the band gap wavelength. If the band gap wavelength is set to a shorter wavelength side than the peak position of the gain spectrum of the semiconductor amplifier, the wavelength of the output light can be made variable over a wider range. The band gap wavelength can be set to an arbitrary value during the manufacturing process.

  Coarse adjustment in the variable wavelength control is performed by the short wave gain region 59 and the long wave gain region 58. Fine adjustment in the wavelength variable control is performed through an electro-optic effect caused by a voltage applied to the PIN junction 61 provided in the second ring optical waveguide 52.

  Next, the operation of the wavelength tunable laser of this embodiment will be described.

  When current is injected into the short wave gain region 59 and the long wave gain region 58 of the semiconductor amplifier 501, a part of the pump light is a straight optical waveguide 57, a first ring optical waveguide 55, a linear optical waveguide 56, and a second ring type. The light propagates in the order of the optical waveguide 52 and the straight optical waveguide 53. Then, it is reflected by the highly reflective end face 54 and returns to the semiconductor amplifier 501 again to induce stimulated emission to increase the number of photons. Some of the induced photons are reflected by the end face 64 of the semiconductor amplifier 501 and input again to the planar optical circuit 51. Thereafter, the light propagates back and forth within the semiconductor amplifier 501 and the planar optical circuit 51. Laser oscillation occurs when the rate of increase in the number of photons due to stimulated emission is greater than the rate of decrease in the number of photons due to the propagation loss inside the semiconductor amplifier 501 and the planar circuit and the mirror loss at the reflection end face. Laser light is emitted from the end face 64.

  In the wavelength tunable laser of this embodiment, the wavelength tunable resonator and the gain medium are monolithically integrated on the same semiconductor substrate. Therefore, the load for optical coupling adjustment at the time of module assembly is greatly reduced, and the cost reduction and the yield improvement of the mounting process are greatly advanced.

  The wavelength tunable laser according to the present embodiment is provided with a semiconductor ring optical waveguide having a PIN junction as a wavelength tunable resonator on the same semiconductor substrate. Further, a plurality of gain media having different gain spectrum wavelength regions are cascaded as variable gain media. Therefore, it is possible to realize a wavelength tunable laser function on one semiconductor substrate, and it is not necessary to assemble complex modules when manufacturing a hybrid product in which both a resonator and an amplifier are mounted. Can be planned.

(Fourth embodiment)
The present embodiment relates to a wavelength tunable laser module using the wavelength tunable laser according to any one of the first to third embodiments. Here, the case of the wavelength tunable laser according to the first embodiment will be described.

  FIG. 10 is a block diagram showing a configuration example of the wavelength tunable laser module.

As shown in FIG. 10, the wavelength tunable laser module includes a multiple ring resonator 203, a multiple ring resonator control circuit 208 that controls the multiple ring resonator 203, a first semiconductor amplifier 202, and a second semiconductor amplifier 207. A semiconductor amplifier control circuit 204 for controlling the optical gain of these semiconductor amplifiers, a collimator lens 205 for converging the oscillated laser light, and a single mode fiber 206 for guiding the converged laser light to the outside. It is the composition which has. These configurations are filled with N ₂ and housed in an airtight package 201.

  Next, a driving method of the wavelength tunable laser by the wavelength tunable laser module will be described.

  The semiconductor amplifier control circuit 204 generates an optical gain necessary for spectrum generation in a predetermined semiconductor amplifier among a plurality of semiconductor amplifiers corresponding to a desired wavelength to be set. Current injection is performed so as not to cause optical loss, and a predetermined semiconductor amplifier is gain-operated. The control circuit 208 for multiple ring resonators adjusts the oscillation wavelength of the multiple ring resonator corresponding to a desired wavelength.

  The desired wavelength value may be set in advance in each control circuit during the manufacturing process, or may be set from the outside via wiring (not shown) after the wavelength tunable laser module is manufactured. In the wavelength tunable laser driving method of the second embodiment or the third embodiment, the semiconductor amplifier control circuit 204 controls the optical gain for a plurality of gain media instead of a plurality of semiconductor amplifiers. Since other than this is the same as the case described above, detailed description thereof is omitted.

It is a schematic diagram which shows one structural example of the wavelength variable laser of 1st Embodiment. It is a schematic diagram for demonstrating the principle of the wavelength variable laser of 1st Embodiment. It is the schematic diagram showing the loss spectrum of the transmitted light intensity of a wavelength variable filter. It is the schematic diagram showing the outline of the gain spectrum of a gain variable medium. It is the schematic showing the loss spectrum of the wavelength variable external resonator of a planar optical circuit. It is the schematic which shows the gain spectrum of two semiconductor amplifiers. It is the schematic which shows the gain spectrum of two semiconductor amplifiers. It is a schematic diagram which shows one structural example of the wavelength variable laser of 2nd Embodiment. It is a schematic diagram which shows one structural example of the wavelength variable laser of 3rd Embodiment. It is a block diagram which shows the wavelength tunable laser module using the wavelength tunable laser of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st semiconductor amplifier 4 2nd semiconductor amplifier 46 Wavelength variable filter 59,102 Short wave gain area | region 58,103 Long wave gain area | region

Claims (14)

A wavelength tunable filter for changing the wavelength of the spectral peak of the transmitted light intensity;
A plurality of semiconductor amplifiers optically coupled to the tunable filter and having different gain spectrum wavelength regions;
A tunable light source. The tunable light source according to claim 1,
The wavelength tunable filter is a multiple ring resonator in which a plurality of ring resonators having different optical path lengths are optically coupled,
The plurality of semiconductor amplifiers include: a first semiconductor amplifier that generates a gain spectrum in a predetermined wavelength region; and a second semiconductor amplifier that generates a gain spectrum in a wavelength region different from the gain spectrum of the first semiconductor amplifier. Have
One of both ends of the waveguide of the multiple ring resonator is optically coupled to one of both ends of the waveguide of the first semiconductor amplifier, and the other is both ends of the waveguide of the second semiconductor amplifier. Optically coupled to one of the
An optical thin film having a reflectivity lower than a predetermined value is provided on the other end of the waveguide of the first semiconductor amplifier,
A wavelength tunable light source, wherein an optical thin film having a reflectance higher than the predetermined value is provided on the other end of the waveguide of the second semiconductor amplifier. The tunable light source according to claim 1 or 2,
A wavelength tunable light source in which a heater for changing a temperature of a core layer of a waveguide of the ring resonator is provided in a predetermined range from the waveguide of the ring resonator. A wavelength tunable filter for changing the wavelength of the spectral peak of the transmitted light intensity;
A semiconductor amplifier optically coupled to the wavelength tunable filter, wherein a plurality of gain media having different wavelength regions of the gain spectrum are disposed along the waveguide direction;
A tunable light source. The tunable light source according to claim 4,
The wavelength tunable filter is a multiple ring resonator in which a plurality of ring resonators having different optical path lengths are optically coupled,
One of the two ends of the waveguide of the semiconductor amplifier is optically coupled to one of both ends of the waveguide of the multiple ring resonator, and the other is an optical thin film having a reflectance higher than a predetermined value. Is provided,
A wavelength tunable light source, wherein an optical thin film having a reflectance lower than the predetermined value is provided on the other end of the waveguide of the semiconductor amplifier. The tunable light source according to claim 4 or 5,
A wavelength tunable light source in which a heater for changing a temperature of a core layer of a waveguide of the ring resonator is provided in a predetermined range from the waveguide of the ring resonator. The tunable light source according to claim 4 or 5,
The multiple ring resonator is composed of a planar optical circuit made of a semiconductor material,
A wavelength tunable light source in which a PIN junction structure for changing a refractive index of a core layer of a waveguide of the ring resonator by applying an electric field is provided in the waveguide of the ring resonator. The tunable light source according to claim 4 or 5,
The multiple ring resonator and the semiconductor amplifier are monolithically integrated on the same semiconductor substrate;
The band gap wavelength of the core layer of the semiconductor optical waveguide constituting the multiple ring resonator is set to a wavelength side shorter than the peak position of the gain spectrum of the semiconductor amplifier,
A wavelength tunable light source in which a PIN junction structure for changing a refractive index of a core layer of a waveguide of the ring resonator by applying an electric field is provided in the waveguide of the ring resonator. The wavelength tunable light source according to claim 2 or 3,
A control circuit for a multiple ring resonator for controlling the multiple ring resonator;
A semiconductor amplifier control circuit for controlling the optical gain of the plurality of semiconductor amplifiers;
A tunable light source module. The tunable light source module according to claim 9,
The semiconductor amplifier control circuit generates an optical gain necessary for spectrum generation in a predetermined semiconductor amplifier among the plurality of semiconductor amplifiers corresponding to a desired wavelength, and a semiconductor amplifier excluding the predetermined semiconductor amplifier Current injection is performed so as not to cause optical loss, and the predetermined semiconductor amplifier is gain-operated,
The tunable light source module, wherein the control circuit for the multiple ring resonator adjusts an oscillation wavelength of the tunable filter corresponding to the desired wavelength. The variable wavelength light source according to any one of claims 5 to 8,
A control circuit for a multiple ring resonator for controlling the multiple ring resonator;
A control circuit for a semiconductor amplifier for controlling an optical gain of a plurality of gain media of the semiconductor amplifier;
A tunable light source module. The tunable light source module according to claim 11,
The semiconductor amplifier control circuit generates an optical gain necessary for generating a spectrum in a predetermined gain medium among the plurality of gain media corresponding to a desired wavelength, and a gain medium excluding the predetermined gain medium Current injection is performed so as not to cause optical loss, and the predetermined gain medium is gain-operated,
The tunable light source module, wherein the control circuit for the multiple ring resonator adjusts an oscillation wavelength of the tunable filter corresponding to the desired wavelength. A driving method of a wavelength tunable light source according to any one of claims 1 to 3,
A current is generated so that an optical gain necessary for spectrum generation is generated in a predetermined semiconductor amplifier among the plurality of semiconductor amplifiers corresponding to a desired wavelength, and an optical loss is not generated in the semiconductor amplifiers other than the predetermined semiconductor amplifier. Performing an injection to gain operation of the predetermined semiconductor amplifier;
A method for driving a wavelength tunable light source, wherein an oscillation wavelength of the wavelength tunable filter is adjusted in accordance with the desired wavelength. A driving method of a wavelength tunable light source according to any one of claims 4 to 8,
A current is generated so that an optical gain necessary for generating a spectrum is generated in a predetermined gain medium among the plurality of gain media corresponding to a desired wavelength, and an optical loss is not generated in gain media excluding the predetermined gain medium. Performing the injection to gain operation of the predetermined gain medium;
A method for driving a wavelength tunable light source, wherein an oscillation wavelength of the wavelength tunable filter is adjusted in accordance with the desired wavelength.

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