KR101885782B1 - Wavelength tunable optical transmitter - Google Patents

Abstract

A wavelength tunable transmitter structure using a liquid crystal based tunable filter is presented. In an external resonator structure formed by a semiconductor laser diode, a collimator lens, a liquid crystal wavelength tunable filter, a first etalon filter, and a partial reflection mirror, a tap filter, a wavelength linear filter, a first photodetector, 2 light receiver is inserted. A second etalon filter may be included at the rear end of the partial reflection mirror to compensate dispersion of the optical path. The transmitter comprises two independent thermoelectric elements and the first thermoelectric element is in a hierarchical structure located in a part of the top plate of the second thermoelectric element. The second thermoelectric element controls the base temperature of the entire transmitter and accommodates a liquid crystal wavelength tunable filter, a first etalon, a partial reflection mirror, and a second etalon on the upper part. The first thermoelectric element serves to adjust the oscillation phase of the external resonator, and houses a semiconductor laser diode, a lens, and a wavelength information extractor on the upper part. The proposed structure is advantageous in that the phase can be precisely adjusted only by the basic component parts constituting the external resonator without introducing a phase control part as in the prior art in order to adjust the oscillation phase of the external resonator. Furthermore, the structure including the broadband wavelength information extractor in the same platform as the resonator enables the temperature sensitivity of the liquid crystal to be realistically controlled by the feedback control.

Description

[0001] Wavelength tunable optical transmitter [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable optical transmitter, and more particularly, to a wavelength tunable optical transmitter and a wavelength tunable optical transmitter applied to a dense wavelength division multiplexing (DWDM) optical communication network. .

In the current optical communication environment, the conditions for the DWDM optical transceiver (OTRx) to be applied to the access network include low cost, wavelength tunable function, maximum speed of 10 Gbps, maximum transmission distance of 40 km, and SFP small form factor pluggable). In particular, research and development has been conducted in various ways from around 2000 to the present to realize wavelength tunable function that is the basis of colorless (wavelength independent) function.

There is a SG-DBR (sampled grating-distributed Bragg reflector) laser structure as a temporary example of a typical method of commercially available wavelength variable DWDM OTRx. In the SG-DBR, a front mirror portion, a gain portion, a phase control portion, and a rear mirror portion are formed of a single InP (Indium Phosphide) single- It is a monolithic integrated external resonator structure. An optical amplifier and an MZ (Mach-Zhender) modulator are integrated in series at the rear end of the SG-DBR front mirror for optical output enhancement and modulation functions required for actual transmission. Currently, 10Gbps transmission rate, 40nm wavelength tunable range, 80km optical fiber transmission distance, SFP + commercial products are available.

DBR (digital supermode-distributed Bragg reflector) structure, MGY (modulated grating Y-branch) structure, SSG-DBR (super-structure-grating distributed Bragg reflector, and a grating assisted codirectional coupler with a sampled rear reflector (GCSR) structure.

However, in the InP single substrate integrated wavelength variable semiconductor chip, the complexity of a control structure in which at least three input variables are controlled in order to set an output light wavelength, the complexity of a control mirror, a reflection mirror, an optical connection unit, The price is very expensive due to the problem of lowering the production yield due to the structural complexity due to the integration of various functions. Thus, it is applied to the metro backbone network having a transmission distance of 80 km or more rather than the near optical network.

In realizing a wavelength tunable light source, a typical system that is roughly classified into a single substrate direct-integrated semiconductor chip is a wavelength tunable external resonator structure, and a wavelength variable function is realized by a simple combination of commercial optical components optimized for each part . The external resonator structure is basically formed of a semiconductor laser diode chip, a lens, a tunable filter, and a partial reflection mirror that perform a light amplification function. The rear surface of the semiconductor laser diode chip is coated with a highly reflective coating (hereinafter referred to as "HR") that reflects 80% or more and an anti-reflective coating (hereinafter referred to as "AR" do. The light output wavelength is selected by the mode having the least loss among the external resonator modes existing in the pass band or the reflection band of the tunable filter, and is oscillated.

The tunable external resonator structure is advantageous in that it can realize a low cost by using already commercialized components, and it can be realized by using a waveguide type grating filter using a thermo-optic effect, an etalon filter using a thermo-optic effect, A fiber Bragg grating filter, a grating filter using mechanical rotation, and a liquid crystal filter using an electric field optical effect.

There is a problem that the wavelength variable range is practically limited to 20 nm or less due to the limit of the precision of temperature control, the influence of external environmental temperature, and the deformation due to polar heat. The wavelength tuning method using mechanical strain or rotation has a large element volume, is susceptible to external environmental vibration and mechanical shock, and has a reproducibility problem.

On the other hand, the Nematic liquid crystal-based tunable filter is capable of varying wavelengths in the range of several tens of nanometers in response to a change in the number of volt-volts, and since the capacitive device is a capacitive device, Since it has a similar structure to the liquid crystal driving method and can be manufactured, it is possible to mass-produce it, and it has been actively studied since the early 2000s.

The transmitter structure proposed based on the tunable liquid crystal is as follows.

The structure presented in US 6,205,159 B1, Newport Corporation, David W. Sesko et al (Filed; Jun. 23, 1998, Date of Patent: Mar. 20, 2001) tunable LC etalon, and mirror. For the phase control, a method of adjusting the mirror position by a piezo-electric transducer instead of an LC phase modulator is proposed. Notably, a fixed etalon and a tunable LC etalon were placed in the cavity to provide SML stability and a structure that facilitates wavelength selection as defined in ITU-T. Tunable etalon FSR is larger than gain medium bandwidth and tunable etalon bandwidth is narrower than fixed etalon FSR, so that single longitudinal mode lasing is maintained. However, the adoption of an additional LC modulator in addition to the tunable LC etalon for the phase control may impose a realistic control over the temperature because LC is sensitive to the temperature change. The method of adjusting the phase by varying the mirror position may be difficult to achieve reliability and low cost because of the mechanical moving part. Also, it is not easy to mass produce LC filter with FWHM (FSR of at least 40nm or more) narrower than fixed etalon FSR (100GHz or 50GHz) as current LC filter production technology.

US 8,483,247 B2, Google Inc., Giacomo Antonio Rossi et al. (PCT Filed: Jun. 30, 2004, Date of Patent: Jul 9, 2013) proposed a structure in which an ECL is formed between the backside of the gain medium and the LC tunable reflector Respectively. In order to facilitate the temperature control of the temperature sensitive LC tunable reflector, we proposed a surface alignment on the TEC. A 45-degree mirror is used for this purpose, so that the cavity has a folded cavity (45-degree bent structure) structure. We also proposed a U-shaped holder structure for efficient LC tunable reflector temperature control. In order to increase the accuracy of temperature control, a hermetic optical feed-through structure Butterfly package was used. For the mode alignment, a method of changing the physical cavity length was selected. For this, a method of interposing a piezoelectric actuator between an LC tunable reflector and a TEC was proposed.

However, the complexity of the proposed structure is higher than that of the rectilinear cavity, and in spite of the improved temperature control structure, when the temperature difference between the LUT (Look Up Table) Since the control repeatability of the ECL system is not guaranteed, a linear filter is separately provided outside the resonator to obtain channel information therefrom. The presence of mechanical drive for phase control can be a hindrance to reliability and cost reduction.

US 2010/0111119 A1, Kenji Sato et al. (PCT Filed: Feb. 6, 2008, Pub. Date: May 6, 2010) applied fixed etalon in the cavity to improve lasing stability and ease of channel selection, Is performed by an LC tunable filter and the mode alignment is performed by a phase adjuster in a gain chip. The key point of this patent is to control the output wavelength by aligning the resonator mode and LC filter peaks with fixed etalon peaks using a dithering method (dither control) and mPD without a wavelength locker. However, in reality, a cavity containing LC etalon is difficult to obtain controllability, and therefore can not be used without a wide-band (for example, 40 nm wavelength) wavelength detector capable of directly acquiring channel information. Also, if accurate information about the relative position of the LC etalon peak, which changes according to the environmental temperature change and the control voltage, can not be obtained based on the fixed etalon peak, the voltage control direction can not be determined.

(Tuned LC-etalon, tunable LC, etalon, Gain chip, Fixed etalon, Tunable LC etalon, Mirror) in US 2010/0322269 A1, COGO OPTRONICS, INC., Jian-Yu Liu (Filed: Jun.17, We proposed LCOS (Liquid Crystal on Silicon) type which can be used to realize ECL and two tunable LC etalon structure with glass on both sides. For the mode control, a gain chip consisting of SOA and phase control section is used.

Et al., Et al., Et al., WLL (two beam splitter, 100GHz FSR) with SOA as a gain medium, US7,940,819 B2, Fujitsu Limited, and Kazumasa Takabayashi et al. (Filed: Aug. 4, 2009, Date of Patent: May 10,2011) Etalon and two mPDs), and the etalon FSR in the cavity etalon and the etalon FSR in the WLL are set such that the WLL output signal shows a discontinuous value when the channel is changed. For each of two etalon1 and etalon2 in the cavity, the temperature is independently adjusted based on the temperature map and the temperature is changed to the channel specified by the Vernier effect. Then, the temperatures of etalon1 and etalon2 are adjusted simultaneously, And suggests a way to match them exactly. We have proposed a method to detect and correct channel discontinuity by using wavelength information detector when the operating point shifts due to time degradation (that is, when temperature map does not match). However, precise temperature control is required for each of the two etalons used in the Vernier method in order to secure a good SML quality (SMSR) and to maintain the stable SML quality (SMSR).

US 7,701,984 B2, Eudyna Devices Inc., Toshio Higashi et al. (Et al.), And wavelength selectable mirrors (Reflected wavelength band) in a gain medium composed of SOA, a semiconductor chip integrating a phase shifter section, a fixed etalon, an LC tunable etalon, Is determined by the coating thickness and the number of layers). Two BS (beam splitter) are used to acquire a part of the ECL output light, and the following three monitoring functions are presented: first, an initial wavelength monitor for selecting a channel using a linear filter and LmPD; A power monitor for measuring the light intensity, and a wavelength information detector for measuring the phase of the mode, which is composed of etalon and mPD. In other words, a monitoring architecture with a broadband wavelength information detector capable of acquiring channel information and a narrowband wavelength information detector capable of acquiring phase information within a given channel is proposed. In addition, we proposed an LC based optical shutter at the output port to prevent the output of unstable output light.

Hereinafter, a conventional wavelength variable light source structure using a liquid crystal wavelength tunable filter will be described with reference to FIGS. 1 to 7. FIG.

In the structure of the variable wavelength light source 100 shown in Fig. 1, a semiconductor laser diode chip 10 (hereinafter referred to as LD), a collimator lens 13, an etalon filter 20, a liquid crystal wavelength tunable filter 21, And a tunable external resonator 14 formed by a tunable filter 22. The back surface 11 of the LD chip 10 is coated with HR that reflects 80% or more, and the front surface 12 of the light outgoing surface is AR coated to reflect less than 1%. The reflectivity of the partial reflection mirror front surface 25 is 10 to 60% reflection coated, and the rear surface 26 is AR coating of 0.2% or less.

The light output direction is the direction of the front surface 12 of the LD chip 10 and the light emitted from the rear surface 11 is not used in the conventional tunable lightwave structure 100 using the liquid crystal wavelength tunable filter 21 of Fig. . In the variable wavelength light source structure 101 of FIG. 2, the light exit direction is the rear surface 11 direction of the LD chip 10. The reflective coating of the backside 11 is in the range of 10 to 60%. In addition, the reflectivity of the front surface 25 of the partial reflection mirror 22 uses a HR coating of 80% or more. The other structures are the same as in Fig.

The conventional tunable light source of FIGS. 1 and 2 uses one thermoelectric element 41 and a temperature sensor 40 for the purpose of thermal stability of the oscillation wavelength and optical output power with respect to changes in the external environment temperature. All the optical components are mounted on the thermoelectric elements 41 and maintained at a constant temperature through closed-loop control using the temperature sensor 40. The thermoelectric element 41 is fixed to the TOSA housing 50 for heat dissipation and is in thermal contact therewith.

The liquid crystal wavelength tunable filter 21 of FIGS. 1 and 2 is connected to an electric wiring 22 and an external square wave generating power source 23 to which an electric square wave signal is inputted. The wavelength band transmitted through the liquid crystal wavelength tunable filter 21 varies depending on the magnitude (Vpeak-to-peak, hereinafter referred to as "Vpp ") of the electric square wave voltage signal applied from the outside and the frequency, And the wavelength variable characteristic can be obtained by selectively oscillating the mode existing in the transmission band of the filter (21). A temporary example of the wavelength tuning characteristic of the liquid crystal wavelength tunable filter 21 is shown in Fig. It is a transmission spectrum graph that passes through a liquid crystal wavelength tunable filter while increasing the magnitude Vpp of the applied frequency 2 kHz square wave voltage signal from 1 V to 12 V. As the Vpp is increased, the transmission wavelength band gradually changes to a short wavelength band. As can be seen from the graph of FIG. 4, the 3dB transmission bandwidth of the liquid crystal wavelength tunable filter 21 is practically not easily 0.8 nm or less, and the external resonance mode interval is usually narrow in the range of 0.05 to 0.3 nm. It is difficult to obtain a side mode suppression ratio (SMSR) of more than 50 dB even if a single mode oscillation occurs, because not only a single mode oscillation is difficult due to the competition of three or more external resonance modes. In order to solve the above problem, the etalon filter 20 having a periodic transmission characteristic with a narrow transmission line width is inserted. The principle of oscillation mode selection will be described with reference to FIG. Some modes existing in the bandwidth of the transmission stack 203 of the etalon filter 20 are selected in the mode 200 of the tunable external resonator 14 and the transmission spectrum of the transmission spectrum 204 of the liquid- The mode 201 existing in the first mode is finally selected to improve the single mode oscillation characteristic. At this time, when the Vpp signal applied to the liquid crystal wavelength tunable filter 21 is increased, the transmission wavelength band 204 is changed to the new transmission wavelength band 205, and a new mode 202 is selected. The etalon filter 20 uses a free spectral range (FSR) of 0.8 nm (100 GHz spacing), 0.4 nm (50 GHz spacing), and 0.2 nm (25 GHz spacing) This is because only the wavelengths corresponding to the wavelength grid defined by the International Telecommunication Union (ITU) can be applied to the DWDM transmission network. In addition, by designing the 3 dB transmission bandwidth of the etalon filter 20 to be smaller than 0.2 nm, the number of external resonance modes existing within the 3 dB transmission bandwidth can be made not more than 3, and a single mode oscillation characteristic can be obtained.

The wavelength stability or wavelength error of the wavelength-tunable light source for communications shall be less than 1/20 of the wavelength grid spacing. As a temporary example, the wavelength stability of a commercial wavelength tunable light source applied to a 100 GHz DWDM optical communication network is less than ± 20 pm. It is a very demanding standard considering external environment temperature change, aging effect (deterioration), mechanical impact, mechanical deformation. In order to solve this problem, the function of extracting wavelength information is included in the tunable light source TOSA, and the wavelength precision required by the communication network is satisfied by monitoring the wavelength information in real time through the closed loop control and finely controlling the wavelength .

1, a tap filter 30 for dividing a part of the power of the outgoing light 33 emitted from the tunable external resonator 14 is included to generate the monitoring light 32. The monitoring light 32 is input to the wavelength extracting unit 31 and used for extracting the emitted light wavelength information, and the remaining light is outputted as the final light output. The structure of the conventional wavelength extracting unit 31 will be described with reference to FIG. The input monitor light 32 is divided into the first split light 315 and the second split light 316 by the tap filter 311. [ The first divided light passes through the etalon filter 313, is input to the first light receiver 314, and the second divided light is input to the second light receiver 312. The first photodetector and the second photodetector generate a current signal proportional to the magnitude of the input optical power. The magnitude of the current signal output from the second photodetector is proportional to the wavelength of the monitoring light 32 and the optical power. The magnitude of the current signal output from the first photodetector is proportional to the optical power of the monitoring light 32. Therefore, if the current signal output from the first photodetector is used as a reference and the current signal output from the second photodetector is divided, only the wavelength information can be extracted. Since the etalon filter 311 has a periodic transmission characteristic, wavelength information can be extracted from the wavelength grid within the communication wavelength band. Typically, the FSR of the etalon filter 311 of the wavelength extracting section 31 is 1.6 nm, 0.8 nm, 0.4 nm, 0.2 nm, and Finesse is used in the range of 2 to 7.

In the conventional tunable light source structure shown in Figs. 1 and 2, means for finely controlling the oscillation wavelength using the wavelength information signal output from the wavelength extracting unit 31 is required. A temporal example of the conventional oscillation wavelength fine control means shown in the United States patent (External resonator type wavelength variable semiconductor laser, US2010 / 0111119) and United States patent (Laser module and method of controlling wavelength of external cavity laser, US7701984 B2) 6]. The LD chip 10 is composed of an optical amplifying section 15 and a phase control section 16. The optical amplifying part 15 is a region where light is generated when a current is applied to the first metal pad 18 from the outside. When the current is applied to the second metal pad 19 from the outside, the phase control unit 16 changes the effective refractive index of the optical waveguide 17 of the phase control unit 16 to control the micro-wavelength of the external resonator. 6, the LD chip 10 is divided into the active region and the passive region. First, the complexity of the semiconductor process is increased, and the price due to the lowering of the yield of the device is increased. When the current is supplied to the phase control unit 16 There arises a problem that optical loss is increased as well as effective refractive index change when injected, which is followed by additional difficulties of wavelength variable control and optical power control.

The wavelength extracting unit 31 based on the etalon filter 313 shown in FIG. 5 does not provide an absolute value with respect to the input wavelength but provides only the wavelength error information with respect to the DWDM ITU target wavelength grid. If the wavelength of the input light changes by more than the wavelength grid interval (for example, 0.8 nm) due to a change in the external environment temperature, the wavelength information extraction function can not be performed. The transmission wavelength of the liquid crystal wavelength tunable filter 21 of FIG. 1 is greatly affected not only by the magnitude of the external applied voltage signal but also by the ambient temperature. As a temporary example, the change in the transmission central wavelength value of the liquid crystal wavelength tunable filter with respect to the environmental temperature is shown in Fig. Deg.] To -420 [deg.] / Deg in an ambient temperature range of 20 to 60 degrees, but becomes -1400 pm / deg in a temperature range of 0 deg. 1, the liquid crystal wavelength tunable filter 21 is mounted on the thermoelectric element 41 where the temperature is kept relatively constant. However, when the actual ambient temperature is varied from 0 to 70 degrees, the TOSA internal ambient temperature changes and the temperature due to insecure thermal contact Gradient, etc., to about 5 degrees. Assuming that the operating temperature is 40 degrees and the rate of change of the transmission wavelength due to the temperature of the liquid crystal wavelength tunable filter 21 is -420 pm / deg, the temperature variation magnitude 5 of the liquid crystal wavelength tunable filter 21 means a wavelength change of about -2 nm do. This means that more than two channels are changed in a 100 GHz DWDM channel. Therefore, in the case of using a filter such as the liquid crystal wavelength tunable filter 21 whose wavelength greatly changes with respect to the environmental temperature, the conventional etalon-based wavelength extraction unit 31 can not be used. If it is used, a structure in which the temperature variation magnitude of the liquid crystal wavelength tunable filter 21 becomes less than 0.5 degrees when the ambient temperature changes from 0 to 70 degrees should be applied. However, considering that the structure of the liquid crystal wavelength tunable filter 21 itself is a structure in which liquid crystal is injected between two glass substrates and is very weak in terms of heat transfer, the liquid crystal wavelength tunable filter 21, It is practically difficult to maintain the temperature change magnitude of the temperature difference of 0.5 degrees or less.

In the conventional tunable light source structure shown in FIGS. 1 and 2, an external modulator is used for high-speed transmission. In the C-band and L-band, which are used for the DWDM optical communication network, the 10-Gbps direct modulation (direct modulation of the LD chip 10) can not be performed for more than 5 km due to dispersion of the optical fiber. This is because of the widened oscillation spectrum due to the chirp of the LD chip 10 which occurs during direct modulation. In the conventional 10 Gbps transmission, an InP-based MZ modulator or an electro-absorption modulator is integrated in the LD chip 10 or used separately, instead of the direct modulation method. However, due to the increase in the price of the device due to the use of the external modulator, it is applied to a long-distance metro backbone network of 80 km or more instead of a low-cost optical access network.

US 6205159 B1 US 8483247 B2 US 2010-0111119 A1 US 2010-0322269 A1 US 7940819 B2 US 7701984 B2

The problems of the prior arts based on the LC tunable etalon to date are as follows.

1) In order to control the phase of the oscillation mode, a method of integrating a phase control section in a semiconductor laser or using another LC modulator or a mechanical driving unit has been proposed. Both of them have been realized as a dedicated device, not a general- And complexity increases in terms of operation, thereby causing problems in commercialization in terms of cost reduction, miniaturization, and reliability.

2) In a monolithically integrated opto-electronic semiconductor chip, the reproducibility of the output value (output wavelength) with respect to the input control parameter (generally current) is guaranteed to a certain level, whereas in the ECL system based on the tunable LC filter, Extremely sensitive to temperature. Therefore, it is difficult to obtain the control repeatability of the ECL system in a realistic temperature control structure. That is, with respect to the same control temperature (TEC control temperature) and voltage, the rage output wavelength may differ depending on the environmental temperature. As a method for overcoming this problem, a wavelength information detector (WLL) capable of extracting lasing wavelength information over a wideband (40 nm) wavelength range is provided. However, since the ECL generally includes a plurality of devices, the optical noise size in the cavity can be largely changed depending on the driving conditions and the temperature environment. As the resolution for the wavelength information increases in proportion to the applied bandwidth of the WLL, And becomes vulnerable to noise. There is no report on commercialization of ECL including WLL that can extract wavelength information over 40nm wavelength bandwidth by overcoming these limitations.

3) As the transmission speed increases, the length of the cavity must be shortened. In addition, DML is required for structural simplicity and low cost. However, the transmission by DML in the C-band and the L-band, which are DWDM transmission bands, is highly influenced by dispersion. In particular, at a high speed of 10 Gbps, the transmission distance is limited to several km or less. CML was proposed as a method to solve this problem, and commercialized products were introduced by applying it. However, since the CML technique needs to be controlled so that the temperature change of the transmission filter and the change of the output wavelength are minimized with respect to the environmental temperature change, the cost of the structure and control is increased and the cost is not reduced. Moreover, there is no suggestion to overcome the disadvantages of DML in conjunction with wavelength tunable ECL structure and function.

 Due to such technical barriers, there is no commercially available Tunable ECL product to date.

The following solution is suggested as means for solving the problem of the wavelength variable external resonator structure based on the conventional liquid crystal wavelength tunable filter described above.

1) We propose a structure to mitigate dispersion effect in advance for high speed long distance DWDM transmission by direct modulation. Two Etalons with the same FSR are placed on the same TEC and the same temperature condition is applied. The first etalon is placed in the cavity and the second etalon is placed in the optical signal out of the cavity. The transmittance peak wavelengths of the two etalons have a predetermined offset do.

This structure uses the negative dispersion characteristic of the second etalon outside the cavity to precompensate the optical signal chirp generated by the direct modulation, thereby mitigating the dispersion effect caused by the optical fiber transmission. This temperature control structure gives the same temperature environment as the first etalon in controlling the peak wavelength position of the second etalon, so the offset between the two peak wavelengths is kept constant due to the simultaneous transitions according to the temperature change. Therefore, it is possible to maintain the transmission quality stably with respect to the environmental temperature change without a separate complicated temperature control facility for the second etalon. The offset between the peak wavelengths of the two etalons can be adjusted by changing the incident angle of the second etalon, with the first etalon peak aligned to the ITU-T grid.

2) In the ECL structure with the dispersion relaxation function described above, a broadband WLL structure capable of extracting output wavelength information over the entire tunable range is presented.

Compared with single-chip tunable semiconductor chip structures, tunable ECLs have a large spatial volume, making it difficult to realize accurate temperature control by TEC. In particular, tunable LC filters are relatively bulky compared to other components in the cavity and generally have low thermal contact efficiency, so it is virtually impossible to maintain a precisely defined temperature for environmental temperature changes. Therefore, the tunable ECL system deviates from the repeatable system, and the output wavelength for the input control values changes depending on the ambient temperature during operation. If the control repeatability is not ensured, the correct output wavelength can not be obtained only by the values of the input control variables for wavelength tuning. In order to overcome this problem, a broadband WLL function capable of extracting output wavelength information over the entire variable wavelength range is indispensably required.

In general, the conventional WLL is based on etalon, and since the wavelength change detection band is very narrow as several tens of GHz, a WLL structure that is different from the conventional one is required. As the wavelength information extraction band narrows for a given optical power change amount, the resolution of the wavelength information improves. Wideband (40nm range) WLL has much worse wavelength resolution than narrow band (less than 0.4nm) WLL, so it can obtain stable channel information by remarkably lowering optical noise.

The implemented WLL is located outside the cavity and monitors the wavelength of the output light output from the cavity. In a conventional structure having a structure in which the inside and the outside of the cavity are linearly coupled, it is acceptable to place the WLL outside the cavity. On the other hand, in the structure in which the cavity and the final output stage are nonlinearly coupled by the second etalon outside the cavity as in the present invention, it is difficult to acquire accurate wavelength information due to distortion due to nonlinear coupling when the conventional method is used .

In the present invention, it is possible to detect a minute mode change in a cavity to continuously maintain the SML phase and the quality (SMSR) in spite of environmental temperature changes in a wavelength variable system in which a cavity and an optical output stage are nonlinearly coupled. We propose a WLL structure that minimizes the influence of optical noise in a cavity so that broadband wavelength information can be extracted.

3) A cost effective phase control method based on stacked dual TEC structure is proposed.

To produce and maintain a good quality SML, it is necessary to align the wavelength of the ECL mode with the peak (s) of the filter (s) in the cavity. To this end, the equipment and mode The equipment to adjust the phase must be established. Needless to say, such an additional facility is designed to increase the complexity of the apparatus to a minimum so that the feasibility is enhanced.

In general, a tunable ECL using an LC filter typically includes a gain medium, a fixed etalon, a tunable LC filter (or reflector), and a mirror. In order to maximize the optical characteristics, it is required to align the lasing mode near the peaks of the filters in the cavity. Previously, a phase control section was added to the gain medium for the phase matching of this mode, or a method of physically changing the position of the mirror using a mechanical driving body was proposed.

The addition of the phase control section to the FP-LD changes the wavelength of the ECL mode by varying the current applied to the phase control section. This method is more advantageous in terms of price, reliability, and volume than the method of aligning modes by changing the physical length of the cavity by a mechanical actuator. However, since the phase control section must be added to the existing FP-LD, it has a problem in that it is inferior in versatility and rises in price compared to a simple FP-LD.

In the present invention, a temperature control structure capable of controlling a mode using a conventional simple FP-LD commercial device is proposed to realize a low-cost tunable ECL. The proposed architecture uses two TECs (TEC1, TEC2). TEC2 is attached to the bottom of the TOSA housing and serves to keep the temperature constant by accommodating fixed etalon, LCF, and mirror on the top plate. The TEC1 is located on the TEC2 top plate and houses the FP-LD, collimating lens, and WLL to control their temperature. In particular, TEC1 allows the ECL mode to be aligned with the etalon peak in the cavity by varying the temperature of the FP-LD. That is, TEC1 adjusts the position of the mode by varying the temperature of the FP-LD based on the WLL output information.

The structure in which a small size TEC1 is stacked on a relatively large size TEC2 expands the flexibility of the temperature control by allowing the two TEC temperatures to be independently controlled independently, resulting in a more precise temperature control capability for TEC1. In addition, since the entire ECL system is accommodated on the TEC2, the physical deformation of the cavity is minimized in response to the temperature change of the TOSA housing due to the ambient temperature change, thereby maintaining a constant SML quality.

4) Based on real-time information on LCF peak position and mode position, we propose a structure that maintains mode and quality of output light by closed loop control.

In general, tunable lasers are controlled based on LUTs. The LUT records the values of the input variables that determine the wavelength for each of the designated wavelengths. In order to maintain a stable 1: 1 correspondence between these input variables and output wavelengths (ie, to be a repeatable system), the temperature of all components of the cavity must be precisely controlled. In addition, physical stress is applied to the cavity according to the ambient temperature, which changes the optical characteristics, which also interferes with reproducibility. Considering realistic price and volume, it is almost impossible to implement a complete repeatable system.

A good thermal contact between the tunable LC filter and the TEC top plate is required, in which case a thermal gradient is created between the TEC thermal contact of the tunable LC filter and the opposite side of the TEC. The temperature of the tunable LC filter on the opposite side of the TEC thermal contact is usually difficult to completely control the temperature of the tunable LC filter when considering the price because the temperature inside the TOSA changes with the ambient temperature change unless the inside of the TOSA is vacuum.

Therefore, it is necessary to control the peak of the tunable LCF by adjusting the voltage according to the environmental temperature change, rather than keeping the temperature of the ECL system to be precise enough to ensure controllability.

The voltage control direction (short or long wavelength direction) of the LCF can be determined only by knowing the current position of the tunable LCF peak based on the fixed etalon peak of the selected channel. In addition, the mode position can be controlled by driving TEC1 by securing the position of the current mode based on the fixed etalon peak. That is, it is required to obtain the relative position of the LCF peak and the relative position information of the mode based on the fixed etalon peak of the currently selected channel.

In the present invention, by locating the wavelength-controlled driving point on the slope of the etalon located in the external resonator, the relative position of the LCF peak and the relative position of the mode are determined based on the fixed etalon peak of the selected channel, We show how to obtain information.

According to one aspect of the present invention, there is provided a liquid crystal display device including a broadband light source LD chip, a collimator lens, a first tap filter, a first optical system including a wavelength extracting section, and a Fabry- A first temperature sensor, a second thermoelectric element, a second temperature sensor, and a submount. The wavelength tunable optical transmitter includes a first optical element, a second optical system, and a first thermoelectric element.

In the wavelength tunable optical transmitter according to the present invention, the first optical system is mounted on the first thermoelectric element, the second optical system is mounted on the submount, and the first thermoelectric element and the submount are mounted on the second thermoelectric element It is good.

In the wavelength tunable optical transmitter according to the present invention, the refractive index of the first optical system is changed by the first thermoelectric element to change the phase of the resonance wavelength of the external resonator.

In the wavelength variable optical transmitter according to the present invention, the wavelength extracting section includes a linear wavelength filter, a first photodetector, and a second photodetector having linear characteristics of transmission and reflection values with respect to an optical wavelength in a communication wavelength band, The reflected light of the linear wavelength filter is input to the first photodetector, and the transmitted light is input to the second photodetector.

In the wavelength tunable optical transmitter according to the present invention, a reflection type laser diode (RLD) or a reflection type semiconductor amplifier (RSOA) having a reflectivity of the back surface of the broadband light source LD chip is 80% or more and a reflectance of the emitting surface is 0.1% , The reflectivity of the partial reflection mirror has a range of 10% to 60%, and the reflectivity of the first tap filter has a reflectivity of 1% to 10%.

In the wavelength tunable optical transmitter according to the present invention, the etalon filter having a FSR value of 0.8 nm, 0.4 nm, and 0.2 nm of the first etalon filter and having a 3 dB transmission bandwidth of less than 0.2 nm is used, The square wave voltage signal amplitude Vpp value for changing the transmission wavelength is smaller than 12V, the 3 dB transmission bandwidth is smaller than 1.6 nm, and the FSR value is larger than 50 nm.

In the wavelength tunable optical transmitter according to the present invention, the second etalon filter is inserted into the second optical system after the partial reflection mirror, and the FSR value of the second etalon filter is equal to the FSR value of the first etalon filter , And the Finesse value ranges from 7 to 14.

In the wavelength tunable optical transmitter according to the present invention, the second etalon filter is mounted on the same submount as the first etalon filter to undergo the same temperature control of the second thermoelectric element.

In the wavelength tunable optical transmitter according to the present invention, the second tap filter and the third photodetector are inserted into the second optical system after the second etalon filter, and the reflectivity of the second tap filter has a value of 1 to 10% .

In the wavelength tunable optical transmitter according to the present invention, the wavelength control driving point is located on the slope in the range of 1 to 3 dB from the transmission peak of the first etalon filter located inside the resonator, The relative positions of the transmission peak and the oscillation mode of the liquid crystal wavelength tunable filter with respect to the first etalon peak can be analyzed.

According to the present invention, it is possible to stably maintain the transmission quality with respect to environmental temperature changes without a separate complicated temperature control facility for the second etalon.

According to the present invention, it is possible to detect minute mode changes in the cavity to continuously maintain the SML phase and the quality (SMSR) in spite of environmental temperature changes in a tunable system in which a cavity and an optical output stage are nonlinearly coupled At the same time, a WLL structure is provided in which the influence of optical noise is minimized while being positioned in the cavity so that 40nm wideband wavelength information extraction is possible.

According to the present invention, the two TEC temperatures are controlled independently of each other, thereby expanding the flexibility for temperature control and providing more precise temperature control capability for TEC1. In addition, since the entire ECL system is accommodated on the TEC2, the physical deformation of the cavity is minimized in response to the temperature change of the TOSA housing due to the ambient temperature change, thereby maintaining a constant SML quality.

According to the present invention, by locating the wavelength-controlled driving point on the slope of the etalon located in the external resonator, the change amount of the optical power within the cavity provided by the wavelength information detector is determined by the relative position of the LCF peak and the mode A method for obtaining relative position information is provided.

1 schematically shows a conventional tunable external resonator light source structure using a liquid crystal wavelength tunable filter,
Fig. 2 is a view schematically showing another form of a conventional tunable external resonator light source structure using a liquid crystal wavelength tunable filter; Fig.
3 is a view for explaining an oscillation wavelength selection principle of a conventional tunable external resonator light source structure using a liquid crystal wavelength tunable filter,
4 is a graph showing a transmission spectrum of a liquid crystal wavelength tunable filter according to the magnitude of an external square wave voltage signal,
5 is a view schematically showing a structure of a conventional wavelength extracting section,
6 is a view schematically showing an LD chip structure in which a phase control section is integrated,
FIG. 7 is a graph showing a change in the transmission central wavelength of the liquid crystal wavelength tunable filter according to the environmental temperature,
8 is a schematic view illustrating a structure of a wavelength tunable transmitter according to an embodiment of the present invention.
9 is a graph showing transmission and reflection characteristics of a linear transmission filter,
10 is a view schematically showing a structure of a wavelength extracting unit using a linear transmission filter,
11 is a graph showing wavelength information characteristics extracted using a linear transmission filter in a tunable wavelength tunable external resonator light source based on a liquid crystal wavelength tunable filter,
12 is a schematic view illustrating a structure of a wavelength tunable transmitter according to an embodiment of the present invention;
13 is a graph showing dispersion characteristics of the etalon filter according to Finesse,
FIG. 14 is a view schematically showing the structure of a wavelength tunable transmitter according to another embodiment of the present invention; FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

Referring to FIG. 8, a description will be given of a structure of a tunable liquid crystal wavelength tunable filter external resonance type TOSA 200 according to the present invention.

A first optical system 45 including a broadband light source LD chip 10, a collimator lens 13, a first tap filter 30 and a wavelength extracting section 60 and a second optical system 45 including a wavelength tunable filter A second optical system 46 including a first thermoelectric element 21, a first etalon filter 20 and a partial reflection mirror 22 and a first thermoelectric element 43, a first temperature sensor 44, 41, a second temperature sensor 40, and a submount 42. The first optical system 45 is mounted on the first thermoelectric element 43 and thermally contacted. The second optical system is mounted on the submount 42. The first thermoelectric element 43 and the submount 42 are mounted on the second thermoelectric element 41 and are thermally contacted with each other. The submount 42 is made of tungsten copper (WCu) or aluminum nitride (AlN), which has excellent heat transfer efficiency, and may have a metal pattern shape for ease of component placement of the second optical system.

The front surface 12 of the broadband light source LD chip 10 is coated with less than 1% antireflection coating and the rear surface 11 is coated with more than 80% The broadband light source LD chip 10 is fabricated on the InP substrate by a combination of III-V or II-VI group elements such as InGaAsP, InGaAlAs and InAlAs and the active layer is a multi-quantum well (MQW) . Typically, such a broadband light source LD chip 10 is referred to as a Reflective Laser Diode (R-LD) or a Reflective Semiconductor Optical Amplifier (R-SOA).

The first tap filter 30 inputs a part of the optical signal 33 emitted from the collimator lens 13 to the wavelength extracting section 60 and transmits the remaining part. The reflectivity of the first tap filter 30 is preferably in the range of 1 to 10%.

And is electrically connected to the external square wave voltage source 23 via the electric wiring 22 in order to vary the transmission wavelength of the liquid crystal wavelength tunable filter 21. The graph of the transmission wavelength change according to the magnitude of the voltage signal of the external square wave voltage source 23 of the liquid crystal wavelength tunable filter is shown in FIG. The FSR value of the Fabry-Perot type liquid crystal wavelength tunable filter 21 is designed to be larger than the gain wavelength band of the LD chip 10, thereby preventing oscillation in the transmission wavelength band of the other orders. Since the gain wavelength bandwidth of the LD chip 10 is usually 40 to 50 nm, the FSR value of the liquid crystal wavelength tunable filter 21 is preferably 50 nm or more. In addition, the 3-dB transmission bandwidth of the Fabry-Perot type liquid crystal wavelength tunable filter 21 is preferably made smaller than 1.6 nm in order to actually isolate the 3-dB transmission bandwidth from the adjacent channel.

The FSR value of the first etalon filter 20 is 0.8 nm (100 GHz wavelength grid spacing), 0.4 nm (50 GHz wavelength grid spacing), 0.2 nm (25 GHz wavelength grid spacing) ) And the like. Also, for stable single-mode oscillation, the outer resonance mode is designed to be three or less within the 3 dB transmission bandwidth of the first etalon filter 20. Considering the outside resonance mode interval in the range of 0.05 nm to 0.2 nm, the 3 dB transmission bandwidth is preferably 0.2 nm or less. The material of the etalon filter may be silicon, glass, LiNbO3, KTP, or the like.

The reflectance of the front surface 25 of the partial reflection mirror 22 is 10 to 60% reflection coated, and the rear surface 26 is AR coated to 0.2% or less. The wavelength tunable external resonator 14 is from the rear surface 11 of the LD chip 10 to the front surface 25 of the partial reflection mirror 22.

The structure of the wavelength extracting unit 60 will be described with reference to FIG. A linear wavelength filter chip 63, a first light receiver 314, and a second light receiver 312. The front side 64 of the linear wavelength filter chip 63 is coated with a linear wavelength filter and the rear side 65 is AR coated below 0.2%. The angle 66 of the light incident on the linear wavelength filter chip 63 for the sake of alignment is in the range of 43 to 47 degrees. The light 316 reflected by the front surface 64 of the line-of-sight wavelength filter chip 63 is detected by the first light receiver 314 and the light 315 transmitted by the second light receiver 312 is detected by the second light receiver 312 . The transmission characteristic graph 61 and reflection characteristic graph 62 of the linear wavelength filter chip 63 are shown in Fig. For use in the C-band wavelength band (1528 ~ 1562nm), it is fabricated to have linear transmission characteristics in the range of 1520 ~ 1570nm. As can be seen from the graph of FIG. 9, the transmission value is 83% and the reflection value is 17% at 1520 nm, the transmission value is 3% and the reflection value is 97% at 1570 nm.

As the wavelength information extraction in the C-band band for optical communication, the transmission (T) and reflection (R) characteristics of the wavelength linear filter of FIG. 9 can be approximated by the following equations (1) and (2).

(1) T (?) = 0.9 - 0.8 占 (? -1530) / 50,

(2) R (?) = 1 - T (?).

In Equation (1) and Equation (2),? Is a wavelength value in nm. It is well known that the above equation (1) is a temporary example, and various linear equations and wavelength ranges are possible. Also, using the following two realistic assumptions

Assumption (1): When an external resonant light source is formed, light having a side-mode suppression ratio (" SMSR ") of more than 50 dB can be approximated to a single wavelength.

Assumption 2: The first light-receiver coupling efficiency of the reflected light 316 of the linear wavelength filter 63 and the second light-receiver coupling efficiency of the transmitted light 315 are the same.

The wavelength information extraction formula is as shown in the following equation (3) using equations (1) and (2).

L (2) + L (1) - 2T (?) - 1 (2)

                        L (1) = first photoreceptor electrical signal

                        L (2) = second receiver signal

The wavelength information signal L (λ) according to equation (3) also changes linearly with respect to wavelength since T (λ) shows a linear characteristic with respect to wavelength in equation (1). The wavelength information extraction formula of the formula (3) can be variously shaped. As an example, the following equations (4), (5), and (6) are possible.

L (λ) = L (1) / L (2) to 1 / T (λ) -1

L (λ) = L (1) / (L (1) + L (2)) to T (λ)

L (λ) = L (2) / L (1) + L (2)

 An example of the wavelength information value relative to the oscillation wavelength obtained by applying the wavelength extracting section 60 to the tunable external resonator 14 of Fig. 8 is shown in Fig. As the oscillation wavelength output from the tunable external resonator 14 of FIG. 8 varies from 1532 nm to 1562 nm, the signal output from the wavelength extracting unit 60 shows a stepped shape. This is because when the transmission wavelength band of the tunable wavelength tunable filter 21 of the tunable external resonator 14 of FIG. 8 is varied, the oscillation wavelength is discontinuously shifted to the adjacent DWDM wavelength channel by the first etalon filter 20 . Characteristics of the wavelength extracting unit 60 in Fig. 11 As an example, channel information of the currently oscillating wavelength can be extracted over the entire used wavelength range.

Another structure of the tunable wavelength tunable TOSA 300 proposed by the present invention will be described with reference to FIG. The basic structure is the same as that of the tunable TOSA 200 of FIG. 8, but a second etalon filter 301 is added to the rear of the partial reflection mirror 22 to constitute the second optical system 47. The second optical system 47 is mounted on the submount 42 and is in thermal contact with the second thermoelectric element 41.

The FSR value of the second etalon filter 301 is equal to the FSR value of the first etalon filter 20, and the Finesse value is designed to pre-compensate dispersion due to the optical fiber transmission distance. A graph of dispersion characteristics according to the Finesse value of the second etalon filter 301 having an FSR of 0.8 nm is shown in Fig. The offset value (?? =? -? Peak) between the transmission wavelength peak value? Peak of the second etalon filter 301 and the light wavelength value? Emitted from the tunable external resonator 14 is the x- Is the calculated dispersion value. Since the optical fiber has a positive value of + 17 ps / nm / km in the C-band wavelength band, a positive Δλ value is used for dispersion compensation using the second etalon filter 301. For example, if the Finesse is 7, the maximum dispersion compensation value is -250 ps / nm, which can compensate the dispersion of the optical fiber by about 15 km. When Finesse is 10, the maximum dispersion compensation value is -510 ps / nm, and dispersion compensation of about 30 km is possible. In case of Finesse 14, the maximum dispersion compensation value is -1000 ps / nm. Do. Then, the oscillation wavelength value is aligned with the second etalon filter 301 so as to be about 10 to 40 pm offset from the lambda peak value.

Referring to Fig. 14, another structure of the liquid crystal wavelength tunable filter tunable TOSA 400 proposed by the present invention will be described. 12, a second tap filter 317 and a third photodetector 316 are added to the rear end of the second etalon filter 301 to form a second optical system 48 ). The second optical system 48 is mounted on the submount 42 and is in thermal contact with the second thermoelectric element 41. The optical signal 34 emitted from the second etalon filter 301 is partly reflected by the second tap filter 317 and is incident on the third photodetector 316 and the remaining optical signal 34 is optically output. The reflectivity of the second tap filter 317 is preferably in the range of 1 to 10%. The third photodetector 316 measures the finally outputted optical power and provides the output optical power information to the user. The optical power information obtained by the wavelength extracting section 60 does not have a linear relationship with the optical power that is output as the optical power information inside the resonator 14 through the actual partial reflection mirror 22. [

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

100, 101: Conventional wavelength variable light source structure
10: Semiconductor laser diode chip
13: Lens
20, 301: etalon filter
21: Fluorescent wavelength tunable filter
24: partial reflection mirror
31, 60: wavelength extracting unit
41, 43: thermoelectric element
30, 317: tap filter
63: linear wavelength filter
312, 314: Receiver

Claims (10)

A wavelength tunable optical transmitter comprising:
A second thermoelectric element attached to the bottom surface of the housing;
A first thermoelectric element which is laminated and mounted on a part of the upper part of the second thermoelectric element (hereinafter, referred to as a 'first region') and is temperature-controlled independently from the second thermoelectric element;
A submount that is stacked and mounted on another part of the upper part of the second thermoelectric element (hereinafter referred to as a 'second area');
A first optical system mounted on the first thermoelectric element and in thermal contact with the first thermoelectric element;
A second optical system mounted on the sub-mount;
A first temperature sensor provided in the first thermoelectric element; And
A second temperature sensor provided in the second thermoelectric element,
Lt; / RTI >
The first optical system includes:
A broadband light source for emitting an optical signal;
A collimator lens for passing an optical signal emitted from the broadband light source;
A first tap filter for inputting a part of the optical signal emitted from the collimator lens to the wavelength extracting unit and transmitting the remaining optical signal; And
And a wavelength extracting unit for extracting wavelength information from the optical signal input by the first tap filter,
And,
The second optical system includes:
A liquid crystal wavelength tunable filter for varying a wavelength band (hereinafter, referred to as 'transmission wavelength band') transmitted according to the magnitude and frequency of a voltage signal applied from the outside;
A first etalon filter for transmitting three or less external resonance modes by applying a transmission wavelength band narrower than a transmission wavelength band of the liquid crystal wavelength tunable filter among the modes selected in the transmission wavelength band of the liquid crystal wavelength tunable filter; And
A partial reflection mirror for reflecting a part of the optical signal and transmitting the remaining optical signal,
And,
Wherein the first optical system and the second optical system form an external resonator,
The wavelength extracting unit may extract,
A linear wavelength filter having a transmission characteristic and a reflection characteristic linearly with respect to an optical wavelength in a communication wavelength band;
A first light receiver to which reflected light of the linear wavelength filter is input; And
And a second light receiver for receiving transmitted light of the linear wavelength filter,
And,
Wherein the first etalon filter discontinuously generates a mode jump to an adjacent dense wavelength division multiplexing (DWDM) wavelength channel by varying a transmission wavelength band of the liquid crystal wavelength tunable filter, As a result, it is possible to extract channel information of the wavelength currently oscillating from the characteristic appearing in the wavelength extracting section to the whole used wavelength range,
Wavelength tunable optical transmitter.


delete In claim 1,
The refractive indices of the wideband light source and the collimator lens provided in the first optical system are changed by the first thermoelectric element to change the phase of the resonance wavelength of the external resonator
Wherein the wavelength tunable optical transmitter is a wavelength tunable optical transmitter.


delete In claim 1,
A reflection type laser diode (RLD) or a reflection type semiconductor amplifier (RSOA) having a reflectivity of the back surface of the broadband light source of 80% or more and a reflectance of the emitting surface of 0.1% or less is used,
The reflectivity of the partial reflection mirror has a range of 10% to 60%
The reflectivity of the first tap filter is 1 to 10% reflectivity
Wherein the wavelength tunable optical transmitter is a wavelength tunable optical transmitter.
In claim 1,
Wherein the FSR value of the first etalon filter is 0.8 nm, 0.4 nm and 0.2 nm, and the 3-D transmission bandwidth is smaller than 0.2 nm,
In the liquid crystal wavelength tunable filter, the rectangular wave voltage signal amplitude Vpp value for the transmission wavelength variable is smaller than 12V, the 3 dB transmission bandwidth is smaller than 1.6 nm, and the FSR value is larger than 50 nm
Wherein the wavelength tunable optical transmitter is a wavelength tunable optical transmitter.
In claim 1,
The second optical system includes:
A second etalon filter inserted into the rear end of the partial reflection mirror
Further comprising:
The FSR value of the second etalon filter is equal to the FSR value of the first etalon filter, and the Finesse value is in the range of 7 to 14
Wherein the wavelength tunable optical transmitter is a wavelength tunable optical transmitter.
In claim 7,
Wherein the second etalon filter is mounted on the same submount as the first etalon filter to receive the same temperature control of the second thermoelectric element
Wherein the wavelength tunable optical transmitter is a wavelength tunable optical transmitter.
In claim 7,
The second optical system includes:
A second tap filter inserted into a rear end of the second etalon filter,
Further comprising:
And the reflectivity of the second tap filter has a value of 1 to 10%
Wherein the wavelength tunable optical transmitter is a wavelength tunable optical transmitter.
In claim 1,
The wavelength control driving point is placed on a slope in the range of 1 to 3 dB from the transmission peak of the first etalon filter located inside the resonator, so that the variation amount of the internal optical power of the resonator provided by the wavelength information detector, Which can analyze the relative positions of the transmission peak and the oscillation mode
Wherein the wavelength tunable optical transmitter is a wavelength tunable optical transmitter.

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