JPH04288891A - Optical wavelength changing laser apparatus - Google Patents

Abstract

PURPOSE:To stabilize the out put power level of laser light whose wavelength is changed by a laser apparatus for changing the wave-length of input signal light. CONSTITUTION:A light wavelength changing laser 1 is controlled by a first controller 2 to change the wavelength lambdai of an input light signal into a wavelength lambdaj. The light signal of the wavelength lambdaj is amplified by a light amplifier 3. The power level of light outputted from the light amplifier 3 is detected by a second controller 4. Thus, the second controller 4 controls the light amplifier 3 so as to make the output power level constant.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength conversion laser device that converts the wavelength of an input optical signal and stabilizes the level of output light. Various studies have been made regarding optical signal transmission systems for optical switching systems and optical subscriber systems in optical communication networks. Among these, by utilizing the broadband characteristics that are an advantage of optical fiber, optical signals of multiple wavelengths can be transmitted simultaneously, so optical wavelengths can be assigned to subscribers and terminals, and the wavelength of the optical signal can be converted according to the destination. A wavelength division multiplexing communication system has been proposed that transmits signals using the same wavelength. In this case, an optical wavelength conversion device that can arbitrarily convert the wavelength of the optical signal is required, and configurations using semiconductor lasers and the like have been researched and proposed.

0002

2. Description of the Related Art An optical wavelength conversion laser that converts the wavelength of an input optical signal and outputs the converted signal has, for example, the configuration shown in FIG.
The basic configuration is a bistable semiconductor laser, and a wavelength control region is provided. The region supplying the currents I1 and I2 forms a gain region, and the region supplying the currents IDBR and IP forms a wavelength control region due to the structure of the distributed feedback active layer. These currents I1, I2, IP
, IDBR are appropriately controlled, a threshold value relationship shown in FIG. 13 occurs between the input power Pin of the optical signal of wavelength λin and the optical output power Pout. That is, the wavelength λin
If the power of the optical signal is lower than the threshold Pth, the laser will not oscillate, so the optical output power will be almost zero. However, if the signal light is input with a power exceeding the threshold Pth, the laser will suddenly start oscillating. Therefore, the wavelength λout (≠λin)
The optical output power Pout is obtained. This output light wavelength λout is mainly determined by the current injected into the wavelength control region.

Furthermore, in order to stabilize the optical output of a general semiconductor laser, a configuration shown in FIG. 14, for example, is known. That is, a drive current is supplied from the drive current controller 44 to the semiconductor laser 41 via the resistor 47, and the semiconductor laser 41
The main light beam from the main light beam is input to the optical fiber 43 as an optical signal, and the monitor light beam is input to the photodiode 42. Since the voltage across the resistor 49 due to the current flowing from the power supply to the photodiode 42 via the resistors 48 and 49 is proportional to the output light level of the semiconductor laser 41,
A differential amplifier 45 compares it with a reference voltage 46, applies the difference as an error signal to a drive current controller 44, controls the drive current of the semiconductor laser 41 so that the error signal becomes zero, and keeps the output light level constant. It is something that becomes.

0004

[Problems to be Solved by the Invention] Current I1 [mA] and optical output [mW] for the gain region at different output wavelengths λout of the optical wavelength conversion laser shown in FIG. 12 described above
The relationship with is shown in FIG. In that case, the output wavelength λout
shows the case of 1.53820 μm and 1.53399 μm. As can be seen from the figure, the optical outputs are different for the same current I1 due to the hysteresis characteristics and the different output wavelengths. The difference is a relative value of 1.4 dB when the optical output is around 1 mW. This degree of difference is almost no problem in a system that directly receives the output light of an optical wavelength conversion laser, but in actual wavelength multiplexing optical communication systems such as switching systems, it The signal is multiplexed with optical signals of different wavelengths and transmitted, distributed to a desired line, or separated using a wavelength selection filter, and the level of the optical signal of a certain wavelength input to the optical receiver is If the wavelength is changed, there is a problem in that a power penalty occurs due to optical signals of other wavelengths.

For example, if the reception level drops by 1.4 dB and the signal/crosstalk ratio due to crosstalk deteriorates from 10 dB to 1.4 dB due to the above-mentioned change in optical output, the power penalty will be approximately 0. 3dB occurs. Due to this deterioration, in a system in which many channels are connected, it is necessary to adjust the distribution of optical signal levels within the system to the channel with the worst condition due to power penalty, etc. Due to variations in output, the system configuration itself, such as the degree of multiplicity, is subject to restrictions.

Therefore, the semiconductor laser 41 in FIG.
It is conceivable to use the optical wavelength conversion laser as an optical wavelength conversion laser, and to perform feedback control by detecting the optical output level of the optical wavelength conversion laser. In that case, the currents I1 and I in the gain region of the optical wavelength conversion laser
If feedback is applied to 2, the gain with respect to the optical input also changes, and the sensitivity characteristic with respect to the optical input level changes, causing a problem that stable operation cannot be expected. Also, if feedback is applied to the currents IP and IDBR in the wavelength conversion region,
As a result, the output wavelength changes, resulting in a problem that a predetermined output wavelength cannot be stably obtained. An object of the present invention is to stabilize the output light level after optical wavelength conversion.

[0007]

[Means for Solving the Problems] The optical wavelength conversion laser device of the present invention will be described with reference to FIG. 1. The optical wavelength conversion laser device of the present invention will be described with reference to FIG. A control section 2, an optical amplifier 3 that amplifies the output light of the optical wavelength conversion laser 1, and a second control section 4 that controls the optical amplifier 3 so as to keep the optical output level of the optical amplifier 3 constant. It is something to be prepared for.

[0008] Furthermore, the signal light is transmitted through an optical wavelength filter having a wavelength pass band that is sufficiently wider than the wavelength band of the signal light from the optical wavelength conversion laser 1 and sufficiently narrower than the wavelength band of the spontaneously emitted light from the optical amplifier 3. Thus, a part of the output light of the optical amplifier 3 can be added to the second control section 4.

Further, the signal light input to the optical wavelength conversion laser 1 is made into TM polarized light with respect to the active layer of this optical wavelength conversion laser 1, and a polarizer is provided that allows only the TE polarized light to pass through the output light of this optical wavelength conversion laser 1. It may be configured such that the signal is input to the optical amplifier 3 via the optical amplifier 3.

Further, the signal light input to the optical wavelength conversion laser 1 is made into TM polarized light for the active layer of this optical wavelength conversion laser 1, and the wavelength-converted output light of the optical wavelength conversion laser 1 which oscillates with TE polarization is converted into a semiconductor. TE for the active layer of a laser optical amplifier
It can be configured to input polarized light.

The optical amplifier 3 may be a wavelength-selective semiconductor laser optical amplifier, and the second control section 4 may control the gain of this optical amplifier with respect to the wavelength.

0012

[Operation] The optical wavelength conversion laser 1 converts the wavelength λi of the input signal light into
is converted into an output wavelength λj according to the driving conditions set by the first control unit 2 and output. The optical amplifier 3 is composed of an optical fiber amplifier or a semiconductor laser optical amplifier,
The output light of the optical wavelength conversion laser 1 is amplified and output, and a part of the output light is branched to a half mirror, an optical coupler, etc. and inputted to the second control section 4. The optical amplifier 3 is controlled so that the light level is constant. Therefore,
Input signal light with wavelength λi is converted into output signal light with wavelength λj, and the output light level is controlled to be constant.

Further, by inputting a part of the output light of the optical amplifier 3 to the second control unit 4 via the optical wavelength filter, the spontaneous emission light included in the output light of the optical amplifier 3 is removed by the optical wavelength filter. Only the wavelength-converted output signal light is input to the second control unit 4, and its output level is made constant.

Furthermore, by inputting the TM polarized signal light into the active layer of the optical wavelength conversion laser 1 and inputting only the wavelength converted output light oscillated with TE polarization to the optical amplifier 3 via the polarizer, this optical amplifier The optical amplifier 3 removes the input signal optical component having the wavelength λi input to the optical amplifier 3, and amplifies only the wavelength-converted output signal having the wavelength λj by the optical amplifier 3, thereby reducing crosstalk between wavelengths.

Further, when a TM polarized signal light is input to the active layer of the optical wavelength conversion laser 1 and a wavelength-changed output light oscillated with TE polarization is input to the active layer of a semiconductor laser optical amplifier, this semiconductor laser optical amplifier , has a gain difference between the TM polarized light and the TE polarized light, and since the gain of the wavelength-converted TE polarized light is large for the output light, the input signal light of wavelength λi and
It is possible to separate the output signal light having the wavelength λj.

Further, the wavelength selective semiconductor laser optical amplifier having the DFB structure has a large gain for a specific wavelength, and by controlling this specific wavelength by the second control section 4, the wavelength-selective semiconductor laser optical amplifier has a large gain for a specific wavelength. It is possible to amplify and output only the signal light of the same wavelength, and to make the output level constant.

[0017]

[Embodiment] FIG. 2 is an explanatory diagram of a first embodiment of the present invention, in which 11 is an optical wavelength conversion laser, 12 is a first control section, and 13 is an explanatory diagram of a first embodiment of the present invention.
14 is an optical amplifier, 14 is a second control section, and 15 is a half mirror. The signal light having the wavelength λi is converted into the wavelength λj by the optical wavelength conversion laser 11 controlled by the first controller 12.
signal light. This signal light of wavelength λj is amplified by the optical amplifier 13 and output. A part of this output light is branched by the half mirror 15 and inputted to the second control unit 14, and the second
The gain of the optical amplifier 13 is controlled by the control section 14 . In this case, the half mirror 15 is connected to the optical amplifier 1 at a ratio as small as possible to the extent that it can be detected by the second control unit 14.
It is preferable to have a configuration in which the three output lights are branched.

The optical wavelength conversion laser 11 is, for example, shown in FIG.
The currents I1, I2, IP, IDBR for the gain control region and the wavelength control region are controlled by the first
The control unit 12 performs control to perform desired wavelength conversion. Even if the output level of the optical wavelength conversion laser 11 changes in accordance with the conversion wavelength, the output level of the optical amplifier 13 is made constant by the second control unit 14 regardless of the conversion wavelength. As a conversion laser device, stable wavelength conversion is possible.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention, and the same reference numerals as in FIG. 2 indicate the same parts. This example is
The half mirror of the first embodiment is an optical coupler 16, and this optical coupler 16 allows the wavelength λj of the optical wavelength conversion laser 11 to be
A part of the output light of the optical amplifier 13 that amplifies the output light of is branched and inputted to the second control section 14.
The optical amplifier 13 is controlled to keep the output level constant. This optical coupler 16 also does not divide the output light of the optical amplifier 13 into 1/2, but distributes the output light of the optical amplifier 13 into 1/2.
It is preferable to adopt a configuration in which the distribution is performed at the smallest possible ratio that can be detected at 4.

FIG. 4 is an explanatory diagram of an optical amplifier, in which 21 is a multiplexer, 22 is a pumping light source, 23 is a rare earth doped optical fiber, and 24 is a demultiplexer. A process in which input light and pump light having a wavelength similar to the wavelength of the input light from the pump light source 22 are multiplexed by the multiplexer 21, input to the rare earth doped optical fiber 23, and propagated through the rare earth doped optical fiber 23. In this process, the rare earth element is excited by the excitation light, and the input light is amplified. Since the amplified output light includes pumping light, the pumping light is split by the demultiplexer 24 and only the amplified signal light is output.

FIG. 5 is an explanatory diagram of a semiconductor laser optical amplifier, and as shown in a schematic cross section, the end faces 28 and 29 are anti-reflection coated surfaces or cleaved surfaces, and the current flowing between the electrodes 26 and 27 is directed to the semiconductor laser. When signal light is input to the active layer 25 from the end face 28 side, laser oscillation is started and amplified output light is output from the end face 29 side. The aforementioned optical amplifier 13 can be an optical amplifier using such a rare earth doped optical fiber or a semiconductor laser optical amplifier.

FIG. 6 is an explanatory diagram of a third embodiment of the present invention, in which the same reference numerals as in FIGS. 2 and 3 indicate the same parts, and 17 is an optical wavelength filter. In this embodiment, a part of the output light of the optical amplifier 13 is branched and passed through the optical wavelength filter 17 to the second branch.
This optical wavelength filter 1 is input to the control unit 14 of
The pass band 7 is sufficiently narrower than the spontaneous emission band of the optical amplifier 13 and wide enough to cover the conversion wavelength band of the optical wavelength conversion laser 11. Therefore,
A portion of the output light including the spontaneous emission light of the optical amplifier 13 corresponding to the signal light is input to the second control unit 14, and the optical amplifier 13 is controlled so that the level thereof is constant. .

FIG. 7 is an explanatory diagram of a fourth embodiment of the present invention, in which the same reference numerals as those in the previous embodiments indicate the same parts, and 18 is a polarizer. In this embodiment, TM polarized signal light is input to the active layer of the optical wavelength conversion laser 11,
Only the TE polarized light from the optical wavelength conversion laser 11 that oscillates with TE polarized light is input to the optical amplifier 13 via the polarizer 18. That is, even if the input signal light with the wavelength λi is converted to the wavelength λj and the TM polarized signal light with the wavelength λi passes through the optical wavelength conversion laser 11, it will be blocked by the polarizer 18 and will not be input to the optical amplifier 13. Since the signal light before wavelength conversion and the signal light after wavelength conversion are reliably separated, and the signal before wavelength conversion is removed, the output level of the wavelength-converted signal light can be made constant. . Therefore, crosstalk between wavelengths when wavelength multiplexed can be reduced.

FIG. 8 is an explanatory diagram of a fifth embodiment of the present invention, in which the same reference numerals as those in the previous embodiments indicate the same parts, and 13A is a wavelength selective semiconductor laser constituting an optical amplifier. It is an optical amplifier. This wavelength selective semiconductor laser optical amplifier 13A has a configuration similar to a distributed feedback (DFB) semiconductor laser, and has wavelength selective characteristics as shown in FIG. The input optical wavelength λi that provides this maximum gain
Since n changes depending on the current or temperature, the first control section 12 controls the optical wavelength conversion laser 11 to convert the wavelength λi to the wavelength λj, and at the same time, the maximum gain is obtained at the converted wavelength λj. The second controller 14 controls the current supplied to the wavelength selective semiconductor laser optical amplifier 13A, or the first controller 12 controls the wavelength selective semiconductor laser optical amplifier 13A by means not shown. The temperature of the converter can be controlled to achieve maximum gain at the converted wavelength λj.

Further, semiconductor laser optical amplifiers have different gain characteristics depending on the polarization of input signal light. For example, as shown in FIG.
0, the gain of TM polarized light is lower than that of TE polarized light, and when the ratio of the supply current to the threshold current is approximately 1, the gain difference between the two is about 8 dB. Therefore, a signal light having a wavelength λi of TM polarization is input to the active layer of the optical wavelength conversion laser 11, and the optical wavelength conversion laser 11 oscillates with TE polarization.
When the output light with the wavelength λj is input to the active layer of the semiconductor laser optical amplifier, the output level of the TM polarized light is lower than that of the TE polarized light of the optical wavelength conversion laser 11
The TM polarization component output from the semiconductor laser optical amplifier is T
It is sufficiently lower than the E polarization component, and the input signal light having the wavelength λi and the converted output light having the wavelength λj can be reliably separated and output.

FIG. 11 is an explanatory diagram of the sixth embodiment of the present invention, in which 31 is an optical splitter, 32-1 to 32-n are optical wavelength selection filters, 33 is an optical combiner, and 11-1 to 11- n is an optical wavelength conversion laser, 12-1 to 12-n are first control units,
13-1 to 13-n are optical amplifiers, and 14-1 to 14-n are second control units. The wavelength multiplexed optical signals with wavelengths λ1 to λn are distributed by the optical splitter 31 to the optical wavelength selection filters 32-1 to 32-n, respectively, and the optical signals with different wavelengths are selectively output, and the optical wavelength conversion lasers 11-1 to 11-n are selectively output. 1
1-n.

Each of the optical wavelength conversion lasers 11-1 to 11-n is converted into a wavelength different from the input wavelength by a first control unit 12-1 to 12-n controlled by a host processor (not shown) or the like. controlled so that Then, the wavelength-converted output light is amplified by optical amplifiers 13-1 to 13-n, and controlled by second control units 14-1 to 14-n so that the output level thereof is constant, and optically synthesized. The signal is input to the device 33. That is, since the level of each wavelength-converted signal light input to the optical combiner 33 is controlled to be constant, there is no deterioration of the power penalty in the optical signal receiving section.

[0028] Also, each control section 12-1 to 12-n, 14-1
It is also possible to share the reference voltage etc. in the optical amplifiers 13-1 to 14-n, and it is possible to make the reference voltage etc. in common among the optical amplifiers 13-1 to 14-n. A configuration may be provided that allows fine adjustment. It is also possible to integrate an optical wavelength conversion laser and an optical amplifier into a single chip, or it is possible to integrate a plurality of optical wavelength conversion lasers and a plurality of optical amplifiers into a single-chip integrated circuit, or to integrate the entire optical wavelength conversion laser into a single chip. It is also possible to integrate it into an integrated circuit. Thereby, it is possible to downsize the device of the wavelength division multiplexing optical communication system.

[0029]

As explained above, the present invention converts the wavelength of input signal light into a desired wavelength in the optical wavelength conversion laser 1, amplifies the output light with the optical amplifier 3, and The second control unit 4 controls the level to be constant.
When various wavelength multiplexing optical communication systems are constructed using an optical wavelength conversion laser 1 whose output level changes depending on the converted wavelength, an optical amplifier 3 that does not affect the wavelength conversion characteristics is used. Since the output level is stabilized using , it has the advantage of being able to perform stable wavelength conversion.

Furthermore, by removing most of the spontaneous emission light contained in the output light of the optical amplifier 3 using an optical wavelength filter and inputting the signal light component to the second control section 4, the output of the wavelength-converted signal light is level can be stabilized. Therefore, there is an advantage that crosstalk between wavelengths can be reduced.

Furthermore, by inputting the TM polarized signal light into the active layer of the optical wavelength conversion laser 1 and inputting the output light of the optical wavelength conversion laser 1 which oscillates with TE polarization into the optical amplifier 3 via the polarizer, Since the input signal light component having the input wavelength λi and the signal light having the conversion wavelength λj can be separated and amplified by the optical amplifier 3, crosstalk between wavelengths can be reduced.

Further, the semiconductor laser optical amplifier has TE polarized light and T
Since it has a gain difference with respect to M-polarized light, the TM-polarized signal light is input to the active layer of the optical wavelength conversion laser 1,
By inputting the output light of the optical wavelength conversion laser 1 that oscillates with TE polarization into the active layer of the semiconductor laser optical amplifier, an input signal light component of input wavelength λi and a converted wavelength λj are generated.
can be separated from the signal light by the gain difference of the semiconductor laser optical amplifier.

Furthermore, by using the optical amplifier 3 as a wavelength-selective semiconductor laser optical amplifier and making the wavelength at which the maximum gain is made coincide with the output wavelength λj of the optical wavelength conversion laser 1, only the signal light having the converted wavelength λj can be used. It has the advantage of being able to amplify and keep the output level constant.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is an explanatory diagram of a first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of an optical amplifier.

FIG. 5 is an explanatory diagram of a semiconductor laser optical amplifier.

FIG. 6 is an explanatory diagram of a third embodiment of the present invention.

FIG. 7 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 8 is an explanatory diagram of a fifth embodiment of the present invention.

FIG. 9 is a characteristic explanatory diagram of a wavelength selective semiconductor laser optical amplifier.

FIG. 10 is a gain characteristic curve diagram depending on polarization of input light of a semiconductor laser optical amplifier.

FIG. 11 is an explanatory diagram of a sixth embodiment of the present invention.

FIG. 12 is an explanatory diagram of an optical wavelength conversion laser.

FIG. 13 is an explanatory diagram of optical output characteristics of an optical wavelength conversion laser.

FIG. 14 is an explanatory diagram of a conventional example.

FIG. 15 is an explanatory diagram of wavelength conversion characteristics of an optical wavelength conversion laser.

[Explanation of symbols]

1 Optical wavelength conversion laser 2 First control section 3. Optical amplifier 4 Second control section

Claims (5)

[Claims] 1. An optical wavelength conversion laser (1) and a first control unit (1) for controlling driving conditions of the optical wavelength conversion laser (1).
2), an optical amplifier (3) for amplifying the output light of the optical wavelength conversion laser (1), and controlling the optical amplifier (3) so as to keep the optical output level of the optical amplifier (3) constant. An optical wavelength conversion laser device comprising: a second control section (4). 2. The wavelength band is sufficiently wider than the wavelength band of the signal light from the optical wavelength conversion laser (1), and the optical amplifier (
3), a part of the output light of the optical amplifier (3) is sent to the second control unit (4) through an optical wavelength filter having a wavelength pass band sufficiently narrower than the wavelength band of the spontaneous emission light from the optical amplifier (3). 2. The optical wavelength conversion laser device according to claim 1, further comprising a configuration in which: 3. Signal light input to the optical wavelength conversion laser (1) is made into TM polarized light with respect to the active layer of the optical wavelength conversion laser (1), and the output light of the optical wavelength conversion laser (1) is Claim 1 characterized in that the light is input to the optical amplifier (3) via a polarizer that allows only TE polarized light to pass through.
The optical wavelength conversion laser device described above. 4. Signal light input to the optical wavelength conversion laser (1) is TM polarized with respect to the active layer of the optical wavelength conversion laser (1), and the optical wavelength conversion laser (1) oscillates with TE polarization. 2. The optical wavelength conversion laser device according to claim 1, wherein the wavelength-converted output light of ) is input to the active layer of the semiconductor laser optical amplifier as TE polarized light. 5. The optical amplifier (3) is a wavelength selective semiconductor laser optical amplifier, and the second control unit (4) controls the gain of the optical amplifier (3) with respect to the wavelength. The optical wavelength conversion laser device according to claim 1.