Abstract: Thermal chirp compensation in a chirp managed laser. In one example embodiment, a method for thermal chirp compensation in a chirp managed laser (CML) includes several acts. First, a first bias condition and temperature is selected. Next, a first thermal chirp compensation signal is generated. Then, the laser is driven by biasing a first input drive signal with the first thermal chirp compensation signal. Next, a second bias condition and temperature is selected. Then, a second thermal chirp compensation signal is generated. Finally, the laser is driven by biasing a second input drive signal with the second thermal chirp compensation signal.

Abstract: In a delay line interferometer inside a demodulator, with respect to polarization states of two split beams of light to be interfered with each other, p polarization and s polarization are reversed by a half beam splitter and, further, again multiplexed by the half beam splitter used for splitting so that interference beams of light are generated.

Abstract: One embodiment provides a system that tests optical performance in an Ethernet passive optical network (EPON), which includes an optical line terminal (OLT) and at least one optical network unit (ONU). The system configures an ONU with a circular queue that contains test frames for testing optical performance. The OLT then notifies the ONU to transmit test frames at a specified data rate for a specified duration. After receiving test frames at the OLT, the system measures frame loss and/or bit error rate based on the received test frames.

Abstract: A duplex optical fiber link is provided that includes two bi-directional optical fiber links. Each of the bi-directional links includes a multimode optical fiber and an optical transceiver connected to each of the ends of each of the fibers. Each of the optical transceivers includes a bi-directional optical multiplexer (MUX) that is configured to simultaneously optically couple optical data signals produced by a laser diode of the transceiver into an end of one of the fibers and to optically couple an optical data signal passing out of the end of one of the fibers onto a photodiode of the transceiver. The laser diodes operate at a data rate of at least 10 Gb/s such that each optical transceiver transmits and receives optical data signals at an aggregate data rate of at least 20 Gb/s. Consequently, the bi-directional duplex optical link has an aggregate data rate of at least 40 Gb/s.

Abstract: A representative optical receiver of the invention receives an optical transverse-mode-multiplexed (TMM) signal through a multimode fiber that supports a plurality of transverse modes. The optical receiver has a plurality of optical detectors operatively coupled to a digital signal processor configured to process the TMM signal to determine its modal composition. Based on the determined modal composition, the optical receiver demodulates each of the independently modulated components of the TMM signal to recover the data encoded onto the TMM signal at the remote transmitter.

Abstract: An optical communication system having an optical transmitter and an optical receiver optically coupled via a multi-path fiber. The optical transmitter launches, into the multi-path fiber, an optical transverse-mode-multiplexed (TMM) signal having a plurality of independently modulated components by coupling each independently modulated component into a respective transverse mode of the multi-path fiber. The TMM signal undergoes inter-mode mixing in the multi-path fiber before being received by the optical receiver. The optical receiver processes the received TMM signal to reverse the effects of inter-mode mixing and recover the data carried by each of the independently modulated components.

Abstract: In communications where synchronization of optical signals containing data is required, a multi-channel optical arrayed time buffer may be used. The time buffer includes multiple delay paths comprising delay elements, some of which can be shared to dispense different delays. In an embodiment, an arrayed waveguide grating (AWG) is illustratively used to route an optical signal to a first delay path, which is returnable to the AWG through the first delay path to be rerouted to a second delay path. The total delay affordable to the optical signal is a function of at least a first delay afforded by a delay element in the first delay path, and a second delay afforded by a delay element in the second delay path. In addition, without returning to the AWG, another optical signal may be routed through the second delay path alone to be afforded the second delay only.

Abstract: A communication device comprises a signal combiner, first storage elements, second storage elements and a controller. The signal combiner is configured to combine overhead information with additional information in forming a frame of a signal. The first storage elements are adapted to receive respective portions of a given block of the overhead information to be applied to the signal combiner, and the second storage elements are coupled between respective ones of the first storage elements and respective inputs of the signal combiner. The controller is operative to monitor a count of portions of the frame as the frame is formed by the signal combiner and to control loading of the portions of the given block of the overhead information into the second storage elements from the first storage elements responsive to the monitored count.

Abstract: A module for routing packets of first and second optical signals comprising first and second inputs (A,B) for receiving the first and second optical signals and first and second outputs (C,D) for the optical signals. The module comprises optical switching means (8) for switching the first optical signal and the second optical signal to either one of the two outputs (C,D), and a correlator module (7). The correlator module comprises at least two optical correlators (9,10,11,12). The correlator module (7) is arranged to generate control signals for controlling the switching means (8) based on destination data in packets of the first and second signals such that if packets of the first and second optical signals overlap, the switching means directs the packet that was received first to the output (C,D) indicated by the destination data of that packet and the overlapping subsequent packet is directed to the other output (C,D) or blocked.

Abstract: The interface circuit of the present invention comprises: a first framer configured to input or output a first standard frame compliant with a first standard to or from a transmission path; and a second framer connected to the first framer and configured to input or output a second standard frame compliant with a second standard from or to an in-device interface. The second framer comprises a second framer transmission section configured to input a transmission data from the in-device interface and generate a second standard frame with the transmission data in a payload.

Abstract: A system for a re-configurable optical de-multiplexer, multiplexer or add/drop multiplexer is provided. A re-configurable de-multiplexer system comprises a wavelength selective switch having an input port, an output port and an internal port; a wavelength division de-multiplexer (WDM) optically coupled to the internal port and a plurality of dropped-channel ports optically coupled to the WDM. The wavelength selective switch receives a plurality of input wavelength-division multiplexed channels from the input port and routes a first subset of the channels to the output port and a second subset of channels to the internal port and then to the WDM. The WDM separates each of the dropped channels to a different respective one of the channel ports.

Abstract: A method, apparatus and system for providing clock and data recovery in a receiver for receiving a high speed coherent polarization division multiplexed optical signal using a digital signal processing block including a spectral domain spatial combiner are provided.

Abstract: Techniques for designing optical devices that can be manufactured in volume are disclosed. In an exemplary an optical assembly, to ensure that all collimators are on one side to facilitate efficient packaging, all collimators are positioned on both sides of a substrate. Thus one or more beam folding components are used to fold a light beam up and down through the collimators on top of the substrate and bottom of the substrate.

Abstract: A tunable optical demultiplexer includes a control circuit and one or more heaters thermally coupled to waveguides of an optical demux. The control circuit is in signal communication with the one or more heaters and includes a processor coupled to a memory. The control circuit is configured to receive an optical channel group (OCG) identification signal and adjust the power delivered to the heaters in response to the OCG identification signal and based on parameter values stored in the memory. The optical demux outputs a plurality of optical signals at a corresponding one of a plurality of outputs. The transmission characteristics of the optical demux are varied depending on the amount of power delivered to the heaters. The varying of the transmission characteristics of the optical demux adjusts the spectral shifting of the plurality of wavelengths output by the optical demux.

Abstract: The invention relates to improvements in or relating to optical networks. Methods and apparatus are disclosed for providing communications services to at least one user. Transmission of an optical signal in the downstream direction is described comprising at least one Wavelength Division Multiplexing channel such that at least one of the channels is an unmodulated channel. The unmodulated channel is arranged to transmit user data from the at least one user in the upstream direction.

Abstract: In the method for processing a signal light from free-space by amplifying said signal for free-space optical communications, wherein the improvement includes the steps of (a) pre-amplifying said signal light with low noise; and (b) coupling said signal light into a multimode filter which reduces coupling losses compared to single mode filters.

Abstract: The present invention provides a remodulating channel selector for a wavelength division multiplexed optical communication system. The remodulating selector receives a WDM input signal, selects a particular optical channel from the WDM signal and places the information from the selected signal onto a newly-generated optical output signal. The wavelength of the output optical signal can be the same as or different from one of the optical channels which comprises the WDM input signal. When used in a WDM optical communication system with remodulators at the transmission input, the remodulating selectors provide complete control over the interfaces with optical transmitters and receivers, permitting use with a broad range of optical equipment.

Abstract: Digital compensation of chromatic dispersion (CD) effect experienced by optical orthogonal frequency-division multiplexed (OFDM) signal in fiber transmission is provided in the frequency domain using a Fast Fourier Transform/Inverse Fast Fourier Transform (FFT/IFFT) pair with equal length of digital samples prior to OFDM receiver signal processing, wherein the equal length is larger than the length of a FFT used for OFDM subcarrier demultiplexing of the received signal. The OFDM signal processing is independent of fiber CD, so small guard-interval (GI) can still be used to achieve high spectral efficiency even under the experience of large CD. The GI need only to be large enough to accommodate other effects such as polarization-mode dispersion.

Abstract: Provided are a channel express/add optical module and a method of channel express/add in an optical add/drop multiplexer node using the channel express/add optical module. The channel express/add optical module comprises: a multiplexer/demultiplexer which demultiplexes a multiplexed optical signal having a plurality of wavelengths into individual wavelength optical signals or multiplexes a plurality of different wavelength optical signals; a plurality of 1×2 switches each of which includes a first output end that guides the demultiplexed different wavelength optical signals to output them thereto and a second output end through which new wavelength optical signals; and a plurality of reflectors each of which reflects the optical signal output to the first output end so that the optical signal is feedback to the multiplexer/demultiplexer via the 1×2 switches.

Abstract: An optical device that includes multiple optical modulators having actual operating wavelengths at a given temperature is described. Because of differences between the actual operating wavelengths and target operating wavelengths of the optical modulators, heating elements may be used to thermally tune the optical modulators so that the actual operating wavelengths match corresponding carrier wavelengths in a set of optical signals. Furthermore, control logic in the optical device may assign the optical modulators to the corresponding carrier wavelengths based at least on differences between the carrier wavelengths and the actual operating wavelengths, thereby reducing an average thermal tuning energy associated with the heating elements.

Abstract: The present disclosure provides optical communication systems and methods that utilize, on top or in place of the conventional framework: (1) optical amplifiers that are provided with extended bandwidth coverage, such as Extended Band Erbium-Doped Fiber Amplifiers (EDFAs), combination of Raman amplifiers and EDFAs, Split-Band C+L EDFAs, etc.

Abstract: A method and apparatus are present for managing a transmission of photons. The number of parameters for transmitting the photons as a beam in a liquid are identified using a number of characteristics of the liquid to form a number of selected parameters. The photons are transmitted in the liquid as the beam to a target using the number of selected parameters to form the transmission of the photons.

Abstract: A universal remote-control signal transmitting device for controlling IR equipment and a setting method thereof. The universal remote-control device uses code identification to perform simple setting. The device includes an IR transmitting circuit and a key control device. The universal remote-control signal transmitting device is also fitted with a single chip processor, an IR receiving circuit and a memory for storing an IR signal code database and programs for analyzing and processing. The setting method includes the steps: 1) receiving codes; 2) calculating; 3) comparing; 4) setting; 5) completing.

Abstract: Disclosed are an RF remote-control device is capable of remotely controlling a plurality of pieces of IR equipment and an RF remote control method. A remote-control device upgrades IR remote-control equipment for RF remote control. A “unified” control method remotely-controls a plurality of pieces of IR equipment using one remote controller. An RF remote controller includes a key device, an MCU 1 and its control circuit, and an RF signal module 1. An RF-IR converter comprises an RF signal module 2, an MCU 2 and its control circuit. An IR transmitting circuit is capable of transmitting infrared signals. The RF signal module 1 corresponds to the RF signal module 2, and the IR transmitting circuit corresponds to the IR equipment. The method is realized mainly by the steps: 1) pairing; 2) pre-storing IR code data; 3) placing; and 4) operating.

Abstract: Transmission-side communication apparatus 100 using a DQPSK (differential quadrature phase-shift keying) scheme is provided with: optical carrier generation section 102 which generates an optical carrier the frequency of which switches among a plurality of different frequencies within one symbol period; and modulation section 103 with which DQPSK-modulates the optical carrier generated by the optical carrier generation means in accordance with a modulation signal at an interval of the symbol period. There are provided: single delay interference section 121 which receives an optical signal obtained by DQPSK-modulating an optical carrier the frequency of which switches among a plurality of different frequencies within one symbol period and outputs an output light obtained by causing the optical signal 104 and a delay optical signal thereof to interfere with each other; and photoelectric conversion section 124 which converts the output light outputted by the delay interference means to an electric signal.

Abstract: The present invention relates to light-based communication, and more particularly it relates to methods for configuration of at least one remote light-sensing device, to a central light-emitting unit and to a light-sensing device. According to the invention, spatial configuration of remote light-sensing devices (e.g. peripherals such as loudspeakers or light devices), will be achieved by transmission of embedded identifiers or configuration information in light emitted in a plurality of directions from a central light-emitting unit. With a different identifier or different configuration information for each direction of transmission, the directions can be distinguished from each other. The invention enables a user to place remote light-sensing devices in a desired spatial position and the central light-emitting unit will be able to determine location and spatial function, i.e. for example whether the peripheral is an audio device and/or a lighting device.

Abstract: The electronic device includes a device housing, an emitter, a receiver, and a reflection structure. The emitter is separated from the device housing and emits an optical signal. The receiver is disposed on the device housing for receiving the optical signal. The reflection structure is formed on the device housing and neighboring to the receiver. When the emitter is disposed in front of the device housing, the optical signal transmitted from the emitter directly reaches the reflection structure and is reflected by the reflection structure, and then the optical signal travels toward the receiver.

Abstract: A system may comprise a single wavelength laser; a modulator optically coupled to said laser; a length of multi-mode fiber optically coupled to said modulator; and a phase mask optically coupled to said fiber. The phase mask may be configured to filter out modes other than a selected mode.

Abstract: The present disclosure provides electrical domain suppression of linear crosstalk in optical communication systems using single-carrier implementations. This electrical domain suppression applies spectral shaping in the electronic radio frequency (RF) domain. Advantageously, spectral shaping in the electronic RF domain transfers system complexity from the bulk optical domain into the highly integrated CMOS (or equivalent) domain. The spectral shaping can include electronic circuitry including an electrical filtering block and a signal linearization block prior to optical modulation. The electrical filtering block suppresses coherent interference terms and can include an RF-domain low pass filter. The signal linearization block linearizes modulator response to compensate spectral regrowth due to nonlinear mixing in the modulator.

Abstract: The present disclosure relates to dispersion slope compensation and dispersion map management systems and methods in an optical network utilizing a reconfigurable optical add-drop multiplexer (ROADM) with a plurality of different values of dispersion compensation modules (DCMs). The DCMs form a dispersion compensation ladder at certain intermediate nodes in the optical network to provide dispersion slope compensation and dispersion map management. The reconfigurable routing structure of the ROADM enables these intermediate nodes to route individual wavelengths to any one of the DCMs as required for the particular path of the wavelength. Advantageously, the present invention removes the requirement for banded compensation at receiver nodes and allows for dispersion map management at intermediate points along a fiber route as opposed to bulk compensation at the receiver.

Abstract: An optical transmitter including a dividing optical coupler for dividing a lightwave onto optical paths; a first optical modulator in a first of the optical paths and driven by an I component of a first signal and a I component of a second signal for modulating the lightwave, a DC bias of the first optical modulator being at a quadrature point; a second optical modulator in a second of the optical paths and driven by a Q component of the first signal and a Q component of the second signal for modulating the lightwave, a DC bias of the second optical modulator being at the quadrature point; a phase shifter for generating a 90 degree phase shift in the Q components of the first and second signals that are modulated by the second optical coupler; and a combining optical coupler for combining the modulated lightwave from the first optical coupler and the phase shifted Q components of the first and second signals for generating a quadrature amplitude modulated signal.

Abstract: A digital coherent receiving apparatus includes a first oscillator for outputting a local light signal of a fixed frequency, a hybrid unit mixing the local light signal with a light signal received by a receiver, a second oscillator for outputting a sampling signal of a sampling frequency, a converter for converting the mixed light signal into digital signal synchronizing with the sampling signal, a waveform adjuster for adjusting a waveform distortion of the converted digital signal, a phase adjustor for adjusting a phase of the digital signal adjusted by the waveform adjustor, a demodulator for demodulating the digital signal adjusted by the phase adjuster, and a phase detector for detecting a phase of the digital signal adjusted by the phase adjuster, and a control signal output unit for outputting a frequency control signal on the basis of the detected phase signal to the second oscillator.

Abstract: A signal processing circuit includes: a first compensator configured to compensate for waveform distortion corresponding to chromatic dispersion of a received optical signal by using digital electrical signals obtained by sampling analog electrical signals by using a sampling signal, the analog electrical signals being obtained by opto-electric conversion of multiple optical signals that include an intensity of the received optical signal and phase information thereon; and a chromatic dispersion compensation controller configured to control a compensation value for the chromatic dispersion in the first compensation from the digital electrical signals in which the chromatic dispersion has been compensated for on the basis of a detected phase offset between the sampling signal and a modulation frequency of the received optical signal.

Abstract: An image forming apparatus is disclosed. The image forming apparatus includes a toner supplying device, a toner container, and a developing device. The toner supplying device supplies toners stored in the toner container to the developing device. The toner supplying device includes a toner tank which stores toners discharged from the toner container, a toner carrying section which carries the toners stored in the toner tank in an obliquely upward direction, and a toner dropping route which causes the toners carried by the toner carrying section to drop into the developing device by toner own weight. The toner carrying section controls an amount of the toners to flow into the toner dropping route.

Abstract: According to an aspect of the invention, an image forming apparatus includes an image forming unit, a first detecting unit, a second detecting unit, a control unit. The image forming unit forms an image on a recording medium by using coloring materials of a plurality of colors based on image information. The first detecting unit detects whether or not the first given number of the first housing units are installed to the apparatus. The second detecting unit detects whether or not the second given number of the second housing unit and the third given number of the first housing unit are installed to the apparatus.

Abstract: An apparatus (100) and method (200) that senses photoreceptor failure in a xerographic printing apparatus is disclosed. The xerographic printing apparatus can include a rotatable photoreceptor (110) having a photoreceptor surface (111), a cleaning device (124) for removing marking material from the photoreceptor, and a printing apparatus controller (150) that controls operations of the xerographic printing apparatus. The method can include charging (220) the photoreceptor surface to a fixed voltage. The method can include discharging (230) at least a portion of the charged photoreceptor surface to an exposed voltage. The method can include developing (240) the discharged portion of the photoreceptor surface by providing a cleaning field between the charged photoreceptor surface fixed voltage and a developing bias voltage. The method can include reducing (250) the cleaning field. The method can include generating (260) a developed image on the photoreceptor using the reduced cleaning field.

Abstract: Multi-color document processing systems and methods are described in which the toner detachment field distribution curve is measured as a function of transfer field and the curve is shifted by adjustment of one or more toner state adjustment actuators to facilitate operation at lower transfer field levels for mitigating retransfer and other high field defects.

Abstract: An image forming apparatus includes a developer bearing body for supplying developer to a surface of the image bearing body, on which an electrostatic latent image is formed by a latent image forming unit; a driving unit for rotating the developer bearing body; a speed control unit for determining a rotation speed of the developer bearing body; a drive control unit for controlling the driving unit so that the developer bearing body rotates at the determined rotation speed; and a control unit for determining the amount of developer to be disposed of on the basis of the determined rotation speed and controlling disposal of the determined amount of developer on the surface of the developer bearing body.

Abstract: An image forming apparatus is configured to give an instruction for unlocking of a cover corresponding to a toner container, from a replacement screen of the toner container displayed when no toner inside the toner container is detected. Further, the image forming apparatus is configured such that the cover corresponding to at least one toner container can be unlocked at a time from the displayed screen.

Abstract: An image fixing assembly includes a heating unit having a heating element and a fusing member enclosing the heating element; a backup member; and a heat conducting member. The fusing member is configured to rotate around the heating element. Further, the fusing member is capable of being heated by the heating element. The backup member is abuttingly coupled to the fusing member for configuring a nip portion therebetween, and is capable of pressing media sheets against the fusing member, when the media sheets pass through the nip portion. The heat conducting member is capable of retractably coupling to one of the fusing member and the backup member for enabling flow of heat between the one of the fusing member and the backup member, and the heat conducting member, for reducing a thermal gradient. Further disclosed is a method for fixing images on the media sheets using the image fixing assembly.

Abstract: A forming-dot counting section counts a number of dots of a subject color based on dot pattern data of the subject color. An overlapping-dot counting section compares the dot pattern data of the subject color and the dot pattern data of at least one other color of which dots are formed prior to the subject color, and counts a number of overlapping dots of the subject color that are formed in an overlapping relation with the dots of the at least one other color. A calculating section calculates the amount of adhering toner of the subject color by subtracting an estimated amount of non-adhering toner from an estimated amount of adhering toner. The estimated amount of adhering toner is estimated based on the number of dots of the subject color. The estimated amount of non-adhering toner is estimated based on the number of overlapping dots.

Abstract: An image forming apparatus includes a rotatable image bearing member for bearing a toner image; a transfer member constituting a transfer portion for transferring the toner image formed on said image bearing member onto a recording material; a voltage source for applying, to said transfer member, a voltage in the form of superimposed DC voltage and AC voltage; controller for controlling said voltage source such that a duty ratio, in the AC voltage, of a component increasing an absolute value of a transfer voltage is less than 50%; and an executing portion for executing an operation in an image forming mode in which the toner image is transferred from said image bearing member onto the recording material with the duty ratio controlled by said controller correspondingly to a kind of the recording material.

Abstract: A fuser and receiver release system and method are provided for improving the release of receivers in high speed of printing systems. This system controls the release of a receiver in conjunction with a fuser in a printing system, and specifically the efficiency and accuracy of the release system. One embodiment of this method includes a belt fuser that allows the separating of the heat transfer and release functions of the fuser such that fuser roller could be made of hard metal core that can be heated to high temperatures without the fear of delaminating elastomeric coatings which are common in roller fusing.

Abstract: An image forming apparatus includes an image carrier; a charging device that charges a surface of the image carrier; an exposure device that forms an electrostatic latent image on the charged surface of the image carrier; a developing device that forms a toner image by transferring toner to the electrostatic latent image from a developing member opposed to the image carrier; and a transfer device that either directly transfers the toner image onto a recording medium or transfers the toner image onto a recording medium after the toner image is temporarily transferred onto an intermediate transfer member.

Abstract: An image forming apparatus, which appropriately performs a banding correction even if similar banding does not always occur at a same position of a recording medium, detects reflected light from a test patch image and obtains information on a density change caused by a periodically-uneven rotation of a rotation member, and performs a density correction at an arbitrary position of a print image based on the acquired information on the density change.

Abstract: An image forming apparatus includes a density sensor that measures density of patch images formed on an image carrier; and a controller that forms patch images having respectively plural density types in which image forming conditions are different respectively and corrects the image forming conditions based on measured density values of the patch images by the density sensor. The controller causes a first irradiation light amount by the light emitting section when measuring patch images whose ratio covered by toner of the image carrier is a prescribed value or more to be set different from a second irradiation light amount by the light emitting section when measuring patch images whose ratio covered by toner of the image carrier is less than the prescribed value.

Abstract: An apparatus includes an image formation unit including a photosensitive drum and a motor for driving the image formation unit. The apparatus acquires a frequency generator signal, which is phase information output from the motor as the motor rotates. In addition, the apparatus corrects unevenness of the density that may occur due to the rotation of the motor according to the acquired phase information.

Abstract: An image forming apparatus has a charging unit which charges an image carrier by applying a voltage to a charging member arranged to be in contact with the image carrier. The image forming apparatus includes an alternating voltage applying unit which generates an alternating voltage, a first voltage detection unit which detects a positive peak voltage of the alternating voltage, a second voltage detection unit which detects a negative peak voltage of the alternating voltage, a voltage amplitude determination unit which determines an amplitude value of the alternating voltage based on the positive peak voltage detected, and an alternating voltage control unit which outputs a signal which changes an output from the alternating voltage applying unit.

Abstract: An image forming apparatus including: a photoreceptor; a charging section to charge the photoreceptor; a developing section to develop a latent image; a transfer section to transfer the developed image to a transfer sheet using a contact transfer method; a cleaning section to remove a remaining toner on the photoreceptor; a control section that performs control so that a toner image is formed in an image forming region, the toner image is transferred to the transfer sheet, and a toner image is formed which is not transferred to the transfer sheet in a region between image forming regions on the photoreceptor; and a charge elimination section provided between the transfer section and the cleaning section; wherein the control section controls polarities of electric current applied to the transfer section and the charge elimination section so that the polarities differ between the image forming region and the region between images.

Abstract: A transfer device comprising: a transfer section which forms a nip portion between the transfer section and an image carrier and transfers a toner image on an image carrier onto a sheet passing through the nip portion; an application section which applies a voltage to the transfer section; a determining section which determines a timing of applying voltage from the application section to the transfer section, wherein the control section controls the application section to apply a voltage having an opposite polarity to a transfer polarity to the transfer section until the timing determined by the determination section in a period since a leading edge of the sheet in a conveyance direction advances into the nip portion until a predetermined non image area of the sheet has passed through the nip portion, and then, at a timing determined, switch to apply a voltage having the transfer polarity.